CI: use hashes for actions/setup-python and actions/checkout

Parrot hashes from SciPy main.

Author: ev-br

.github/workflows/docs.yml

@@ -12,9 +12,9 @@ jobs:
   docs-build:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Set up Python 3.12
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: "3.12"
           cache: "pip"
@@ -45,7 +45,7 @@ jobs:
       pages: write
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Download Artifact
         uses: actions/download-artifact@v4
         with:

.github/workflows/pip.yml

@@ -22,9 +22,9 @@ jobs:
 
     steps:
       # actions/setup-python@v5 has built-in functionality for caching and restoring dependencies.
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@8d9ed9ac5c53483de85588cdf95a591a75ab9f55 # v5.5.0
         with:
           python-version: ${{ matrix.python-version }}
           cache: "pip" # caching pip dependencies