ci: bump actions/checkout from 4 to 6

.github/workflows/cross-platform.yml

@@ -24,7 +24,7 @@ jobs:
           - os: macos-latest
             features: minimal
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
       - name: Build

.github/workflows/nightly.yml

@@ -41,7 +41,7 @@ jobs:
             use_cross: false
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@stable
@@ -79,7 +79,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Download all artifacts
         uses: actions/download-artifact@v4

.github/workflows/release.yml

@@ -44,7 +44,7 @@ jobs:
       version: ${{ steps.parse.outputs.version }}
     steps:
       - name: Checkout
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       - name: Parse tag and verify version
         id: parse
@@ -102,7 +102,7 @@ jobs:
     runs-on: [self-hosted, clean-room]
     steps:
       - name: Checkout
-        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       - name: Authenticate to crates.io (OIDC)
         uses: rust-lang/crates-io-auth-action@b7e9a28eded4986ec6b1fa40eeee8f8f165559ec  # v1.0.3