Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
         uses: astral-sh/setup-uv@v7
         with:
           python-version: "3.14"
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: Build package

.github/workflows/test.yml

@@ -30,7 +30,7 @@ jobs:
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install uv & Python ${{ matrix.python-version }}
         uses: astral-sh/setup-uv@v7
         with:
@@ -54,7 +54,7 @@ jobs:
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install uv & Python ${{ matrix.python-version }}
         uses: astral-sh/setup-uv@v7
         with:
@@ -72,7 +72,7 @@ jobs:
         python-version: ["3.14"]
       fail-fast: false
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install uv & Python ${{ matrix.python-version }}
         uses: astral-sh/setup-uv@v7
         with:
@@ -86,7 +86,7 @@ jobs:
   build-and-check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-tags: true
       - name: Install uv & Python