Bump actions/upload-artifact from 4 to 7 (#10)

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 4 to 7.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v4...v7)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/gradle.yaml

@@ -37,7 +37,7 @@ jobs:
         run: mkdir staging && cp build/libs/ModMail.jar staging && mv staging/ModMail.jar staging/ModMail_$GITHUB_SHA.jar
       - name: Upload jar to Actions
         if: ${{ github.event_name != 'release' }}
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: ModMail_Dev-Build
           path: staging/ModMail_*.jar