Bump actions/checkout from 5 to 6 in /.github/workflows

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -45,7 +45,7 @@ jobs:
 
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up stable toolchain
         if: github.event_name != 'schedule'
@@ -110,7 +110,7 @@ jobs:
             rust-flags: '-C target-feature=+avx -C target-feature=+avx2 -C target-feature=+avx512f -C target-feature=+avx512bw -C target-feature=+avx512vl -C target-feature=+avx512bf16'
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check lints
         uses: ./.github/actions/lints
         with:
@@ -139,7 +139,7 @@ jobs:
           - '-C target-feature=+vfp2 -C target-feature=+d32'
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check lints
         uses: ./.github/actions/lints
         with:
@@ -169,7 +169,7 @@ jobs:
           - '-C target-feature=+neon'
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check lints
         uses: ./.github/actions/lints
         with:
@@ -195,7 +195,7 @@ jobs:
           - '--features=safe_arch'
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check lints
         uses: ./.github/actions/lints
         with:
@@ -226,7 +226,7 @@ jobs:
           - '-C target-feature=+f -C target-feature=+d'
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Check lints
         uses: ./.github/actions/lints
         with:
@@ -300,7 +300,7 @@ jobs:
 
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Cargo doesn't know when to rebuild a target-cpu=native cache when it's
       # migrated across machines, so a CI node must not be exposed to the target