chore: pin GitHub Actions to commit SHAs

Author: r-birkner

.github/workflows/build.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-24.04
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
 
       - name: Install repro-env
         run: |

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-24.04
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
 
       - uses: Swatinem/rust-cache@9d47c6ad4b02e050fd481d890b2ea34778fd09d6