Update actions/checkout digest to 3b9b8c8

Author: renovate[bot]

.github/workflows/rust.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     # actions/checkout@v2
-    - uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938
+    - uses: actions/checkout@3b9b8c884f6b4bb4d5be2779c26374abadae0871
     - uses: actions-rs/toolchain@88dc2356392166efad76775c878094f4e83ff746
       with:
         toolchain: stable
@@ -30,7 +30,7 @@ jobs:
         os: [ ubuntu-latest, macos-latest ]
     steps:
     # actions/checkout@v2
-    - uses: actions/checkout@d632683dd7b4114ad314bca15554477dd762a938
+    - uses: actions/checkout@3b9b8c884f6b4bb4d5be2779c26374abadae0871
     - name: Build
       run: cargo build --tests --verbose
     - name: Run tests