ci: pin GitHub Actions to commit SHAs (supply-chain hardening) (#103)

Every `uses:` is pinned to a full 40-char commit SHA with a trailing
`# vX.Y.Z` comment, replacing floating major tags (and the `release/v1`
branch for gh-action-pypi-publish). A mutable ref can be silently
repointed if an action repo or maintainer account is compromised
(cf. tj-actions/changed-files, March 2025); a SHA pin cannot.

Pins target the latest release of each action, all reviewed this
session. Dependabot (github-actions ecosystem, already configured)
updates SHA pins and bumps the version comment alongside, so security
fixes still arrive as reviewable PRs.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Technologicat

.github/workflows/ci.yml

@@ -17,9 +17,9 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
     - name: Set up Python
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
       with:
         python-version: "3.14"
     - name: Install ruff
@@ -60,9 +60,9 @@ jobs:
             python-version: "pypy-3.11"
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install tools in CI venv
@@ -89,13 +89,13 @@ jobs:
     needs: test
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v6
-      - uses: actions/setup-python@v6
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+      - uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
         with:
           python-version: "3.14"
       - run: pip install build
       - run: python -m build
-      - uses: actions/upload-artifact@v7
+      - uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: dist
           path: dist/
@@ -108,11 +108,11 @@ jobs:
     permissions:
       id-token: write
     steps:
-      - uses: actions/download-artifact@v8
+      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           name: dist
           path: dist/
 
-      - uses: pypa/gh-action-pypi-publish@release/v1
+      - uses: pypa/gh-action-pypi-publish@cef221092ed1bacb1cc03d23a2d87d1d172e277b # v1.14.0
         with:
           packages-dir: dist/

.github/workflows/coverage.yml

@@ -19,9 +19,9 @@ jobs:
         python-version: ["3.12"]
 
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install tools in CI virtualenv
@@ -46,7 +46,7 @@ jobs:
         pdm run python -m coverage run --source=. -m runtests
         pdm run python -m coverage xml
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v6
+      uses: codecov/codecov-action@fb8b3582c8e4def4969c97caa2f19720cb33a72f # v7.0.0
       with:
         token: ${{ secrets.CODECOV_TOKEN }}
         files: ./coverage.xml