security: pin GitHub Actions to valid full commit SHAs

Pins third-party GitHub Actions (`actions/checkout` and `jdx/mise-action`)
to full immutable commit SHAs (`actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683`
and `jdx/mise-action@c2a87611a18de5b3828c5652fe268e992400cb5c`) in CI workflows.
This resolves CI workflow failures and protects against supply chain attacks.

Author: google-labs-jules[bot]

.github/workflows/check.yml

@@ -18,7 +18,7 @@ jobs:
           - "3.12"
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-      - uses: jdx/mise-action@500809d363d3fb4f307ee44f24ef3381a1792a7e # v2
+      - uses: jdx/mise-action@c2a87611a18de5b3828c5652fe268e992400cb5c # v4.3.0
         with:
           tool_versions: |
             python ${{ matrix.python-version }}

.github/workflows/docs.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
-      - uses: jdx/mise-action@500809d363d3fb4f307ee44f24ef3381a1792a7e # v2
+      - uses: jdx/mise-action@c2a87611a18de5b3828c5652fe268e992400cb5c # v4.3.0
       - name: Configure Git Credentials
         run: |
           git config user.name github-actions[bot]