Update actions/checkout action to v4 (#960)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/hakari.yml

@@ -17,7 +17,7 @@ jobs:
     env:
       RUSTFLAGS: -D warnings
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: actions-rs/toolchain@v1
         with:
           toolchain: stable