chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     name: Formatter check
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
 
       - uses: actions-rs/toolchain@v1
         with:
@@ -41,7 +41,7 @@ jobs:
         toolchain: [stable, nightly]
     steps:
       # Checkout the branch being tested
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
 
       # Install rust stable
       - uses: dtolnay/rust-toolchain@master
@@ -71,7 +71,7 @@ jobs:
         toolchain: [stable, nightly]
     steps:
       # Checkout the branch being tested
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v6
 
       # Install python with numpy
       - uses: actions/setup-python@v4