ci: pin third-party GitHub Actions to commit SHAs (#5972)

Replaces every floating tag in our workflow and composite action files
with an immutable 40-character commit SHA, keeping the original `# vX`
comment so Dependabot can still propose version bumps. 186 occurrences
across 25 workflows and 2 composite actions.

Also widens the github-actions Dependabot entry to use the plural
`directories` key with `/.github/actions/*` so composite actions under
`.github/actions/<name>/action.yml` are kept up to date. Previously
Dependabot only scanned `.github/workflows` and the repo-root
`action.yml`, leaving our `python-setup` and `sample-validation-setup`
composite actions unmaintained.

.github/workflows/codeql-analysis.yml

@@ -32,13 +32,13 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
         with:
           persist-credentials: false
 
       # Initializes the CodeQL tools for scanning.
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@v4
+        uses: github/codeql-action/init@9e0d7b8d25671d64c341c19c0152d693099fb5ba # v4
         with:
           languages: ${{ matrix.language }}
           # If you wish to specify custom queries, you can do so here or in a config file.
@@ -51,7 +51,7 @@ jobs:
       # Autobuild attempts to build any compiled languages  (C/C++, C#, Go, or Java).
       # If this step fails, then you should remove it and run the build manually (see below)
       - name: Autobuild
-        uses: github/codeql-action/autobuild@v4
+        uses: github/codeql-action/autobuild@9e0d7b8d25671d64c341c19c0152d693099fb5ba # v4
 
       # ℹ️ Command-line programs to run using the OS shell.
       # 📚 See https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsrun
@@ -64,6 +64,6 @@ jobs:
       #     ./location_of_script_within_repo/buildscript.sh
 
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@v4
+        uses: github/codeql-action/analyze@9e0d7b8d25671d64c341c19c0152d693099fb5ba # v4
         with:
           category: "/language:${{matrix.language}}"