Update runtime workflow to use HEAD commit

This updates the CI workflow for the runtime build and tests to use the
HEAD commit of the PR branch rather than the Fake News merge commit
that the actions/checkout workflow baffingly defaults to.

Testing against the merge commit never made sense to me as a behavior
because as soon as someone updates upstream, it's out of date anyway.

It should just match the exact commit that the developer pushed, and the
once that appears in the GitHub UI.

.github/workflows/runtime_build_and_test.yml

@@ -25,6 +25,8 @@ jobs:
       matrix: ${{ steps.set-matrix.outputs.result }}
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/github-script@v7
         id: set-matrix
         with:
@@ -42,6 +44,8 @@ jobs:
         flow_inline_config_shortname: ${{ fromJSON(needs.discover_flow_inline_configs.outputs.matrix) }}
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -64,6 +68,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -88,6 +94,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -139,6 +147,8 @@ jobs:
     continue-on-error: true
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -166,6 +176,8 @@ jobs:
         release_channel: [stable, experimental]
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -242,6 +254,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -272,6 +286,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -317,6 +333,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -350,6 +368,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -380,6 +400,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -419,6 +441,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -480,6 +504,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -528,6 +554,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -562,6 +590,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -603,6 +633,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.head_ref }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'