Bump actions/checkout from 5 to 6

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/audit.yml

@@ -29,7 +29,7 @@ jobs:
         run: rustc --version
       - run: cargo install cargo-audit
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - run: cargo generate-lockfile

.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install toolchain
@@ -58,7 +58,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install toolchain
@@ -89,7 +89,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install toolchain
@@ -112,7 +112,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install toolchain
@@ -141,7 +141,7 @@ jobs:
         run: rustc --version
       - run: cargo install cargo-deny
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - run: cargo generate-lockfile
@@ -160,7 +160,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Install toolchain