chore(ci): Set continue-on-error to true in all cases (#4678)

Stopping running tests on the first failure is an optimization that
favors fast linters and masks more important failures like unittests and
integration tests.

First time contributors might not know how to run tests locally, and forcing
them to iterate on formatting issues is senseless if the same code is causing
integration failures.

Always run all the tests, even if some fail. This allows anybody to get
the full picture of all failing tests and prioritize their iteration
accordingly.

.github/workflows/unit.yml

@@ -13,26 +13,23 @@ defaults:
 jobs:
   unittests:
     strategy:
+      fail-fast: false
       matrix:
         python-version: ["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"]
         toxenv: [py3]
         experimental: [false]
         check-latest: [false]
-        continue-on-error: [false]
         include:
           - python-version: "3.6"
             toxenv: lowest-supported
-            continue-on-error: false
             check-latest: false
             experimental: false
           - python-version: "3.13-dev"
             toxenv: py3
             check-latest: true
             experimental: true
-            continue-on-error: true
     name: unittest / ${{ matrix.toxenv }} / python ${{matrix.python-version}}
     runs-on: ubuntu-20.04
-    continue-on-error: ${{ matrix.experimental }}
     steps:
       - name: "Checkout"
         uses: actions/checkout@v4