build(deps): 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](https://github.com/actions/checkout/compare/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] <support@github.com>

.github/workflows/bleeding.yml

@@ -31,7 +31,7 @@ jobs:
         - /home/runner/work/_temp/:/home/runner/work/_temp/
       options: --privileged --tty
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Set up problem matchers

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
           - testenv: actionlint
           - testenv: package
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - uses: actions/cache@v4
@@ -106,7 +106,7 @@ jobs:
         - /home/runner/work/_temp/:/home/runner/work/_temp/
       options: --privileged --tty
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Set up problem matchers
@@ -217,7 +217,7 @@ jobs:
             python: "3.14"
     runs-on: "${{ matrix.os }}"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - uses: actions/cache@v4
@@ -285,7 +285,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Initialize CodeQL

.github/workflows/docker.yml

@@ -16,7 +16,7 @@ jobs:
           - archlinux-webengine
           - archlinux-webengine-unstable
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v6
         with:
           python-version: '3.x'

.github/workflows/nightly.yml

@@ -37,7 +37,7 @@ jobs:
     runs-on: "${{ matrix.os }}"
     timeout-minutes: 45
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Set up Python

.github/workflows/recompile-requirements.yml

@@ -18,7 +18,7 @@ jobs:
     timeout-minutes: 20
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Set up Python 3.9

.github/workflows/release.yml

@@ -62,7 +62,7 @@ jobs:
             console.log(`sorted: ${sorted}`);
             return sorted.at(-1);
           result-encoding: string
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v6
         with:
@@ -78,7 +78,7 @@ jobs:
             git config --global user.name "qutebrowser bot"
             git config --global user.email "bot@qutebrowser.org"
       - name: Switch to release branch
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ steps.find-branch.outputs.result }}
       - name: Import GPG Key
@@ -163,7 +163,7 @@ jobs:
     permissions:
       contents: write  # To upload release artifacts
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: v${{ inputs.release_type == 'reupload' && needs.prepare.outputs.version_x || needs.prepare.outputs.version }}
       - name: Set up Python