Update actions/checkout action to v6 (#106)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: David Newhall II <david@sleepers.pro>

Author: renovate[bot]

.github/workflows/codetests.yml

@@ -13,7 +13,7 @@ jobs:
         os: [macos, windows, ubuntu]
     runs-on: ${{ matrix.os }}-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
         with:
           go-version: stable