Update the release PR workflow & add a release-it workflow, too

Now the workflow for releasing this crate is:

1. Trigger the "Create release PR" workflow with the right version,
2. fix up anything in the release PR (e.g. changelog)
3. squash&merge that PR
4. Another workflow triggers that will tag the release & publish to
   crates.io at the version just released.

.github/workflows/release_it.yml

@@ -0,0 +1,41 @@
+name: Cut a new release
+on:
+  pull_request:
+    types:
+      - closed
+
+jobs:
+  tag_github_release:
+    if: github.event.pull_request.merged == true && contains(github.event.pull_request.labels.*.name, 'release')
+
+    permissions:
+      id-token: write # Enable OIDC
+      contents: write
+
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo merge commit is $GITHUB_SHA, from PR branch ${{ github.event.pull_request.head.ref }}
+      - uses: actions-ecosystem/action-regex-match@v2
+        id: version
+        with:
+          text: ${{ github.event.pull_request.head.ref }}
+          regex: "^release/([^/]+)/(.+)$"
+          # Name of crate is steps.version.outputs.group1, version is steps.version.outputs.group2.
+          # TODO: figure out how this works with workspaces & multiple crates
+
+      - name: Create release v${{steps.version.outputs.group2}}
+        uses: softprops/action-gh-release@v1
+        with:
+          tag_name: v${{ steps.version.outputs.group2 }}
+          name: ${{steps.version.outputs.group1}} v${{ steps.version.outputs.group2 }}
+          target_commitish: ${{github.sha}}
+
+      - name: Install stable toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+
+      - run: cargo publish --token ${CRATES_TOKEN}
+        env:
+          CRATES_TOKEN: ${{ secrets.CRATESIO_RELEASE_TOKEN }}

.github/workflows/release_pr.yml

@@ -15,15 +15,31 @@ jobs:
       contents: write
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: chainguard-dev/actions/setup-gitsign@main
       - name: Install cargo-release
-        uses: taiki-e/install-action@v1
+        uses: taiki-e/cache-cargo-install-action@v1
         with:
           tool: cargo-release
+      - name: Install cargo-semver-checks
+        uses: taiki-e/cache-cargo-install-action@v1
+        with:
+          tool: cargo-semver-checks
 
       - uses: cargo-bins/release-pr@v2
+        id: pr
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           version: ${{ inputs.version }}
           check-semver: true
+          crate-release-all: true # all in workspace
+      - uses: actions-ecosystem/action-regex-match@v2
+        id: pr-id
+        with:
+          text: ${{ steps.pr.outputs.pr-url }}
+          regex: "/pull/([0-9]+)$"
+      - uses: actions-ecosystem/action-add-labels@v1
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          labels: release
+          number: ${{ steps.pr-id.outputs.group1 }}