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/run-tests.yml

@@ -11,7 +11,7 @@ jobs:
           - 2021.3.16f1
           - 2020.3.43f1
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ inputs.ref }}
 
@@ -52,7 +52,7 @@ jobs:
           - { version: "2021.3.16f1", changeset: "4016570cf34f" }
           - { version: "2020.3.43f1", changeset: "75bff06b76bf" }
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ inputs.ref }}
 
@@ -90,7 +90,7 @@ jobs:
           - { version: "2021.3.16f1", changeset: "4016570cf34f" }
           - { version: "2020.3.43f1", changeset: "75bff06b76bf" }
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           ref: ${{ inputs.ref }}
 

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Install node package, `unity-verify-code`
       run: npm install --global unity-verify-code