ci: pin external GitHub Actions

Author: devkoriel

.github/workflows/tests.yaml

@@ -5,12 +5,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout repository and submodules
-      uses: actions/checkout@v2
+      uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5
       with:
         submodules: recursive
 
     - name: Install Foundry
-      uses: foundry-rs/foundry-toolchain@v1
+      uses: foundry-rs/foundry-toolchain@c7450ba673e133f5ee30098b3b54f444d3a2ca2d
       with:
         version: nightly