Bump actions/upload-artifact from 6 to 7

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 6 to 7.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v6...v7)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/checkstyle.yml

@@ -28,7 +28,7 @@ jobs:
             - name: Run checkstyle
               run: ./gradlew clean checkstyleMain
             - name: Upload checkstyle report
-              uses: actions/upload-artifact@v6
+              uses: actions/upload-artifact@v7
               if: success()
               with:
                   name: checkstyle-report

.github/workflows/java-21-builds.yml

@@ -40,7 +40,7 @@ jobs:
             - name: Build Skript and run test scripts
               run: ./gradlew clean customTest -PtestEnvs="${{ matrix.envs }}" -PtestEnvJavaVersion=21
             - name: Upload Nightly Build
-              uses: actions/upload-artifact@v6
+              uses: actions/upload-artifact@v7
               if: success() && matrix.id == 1
               with:
                   name: skript-nightly