Bump actions/upload-artifact from 5 to 6 (#25872)

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 5 to 6.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/ci_build_major_branch_keymap.yml

@@ -62,7 +62,7 @@ jobs:
           echo "targets=$(jq -c 'keys' targets.json)" >> $GITHUB_OUTPUT
 
       - name: Upload targets json
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: targets-${{ inputs.keymap }}
           path: targets.json
@@ -112,7 +112,7 @@ jobs:
           qmk mass-compile -t -j $NCPUS -e DUMP_CI_METADATA=yes $(jq -r '.["${{ matrix.target }}"].targets' targets.json) || touch .failed
 
       - name: Upload binaries
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: firmware-${{ inputs.keymap }}-${{ matrix.target }}
           if-no-files-found: ignore
@@ -146,7 +146,7 @@ jobs:
           merge-multiple: true
 
       - name: Upload all firmwares
-        uses: actions/upload-artifact@v5
+        uses: actions/upload-artifact@v6
         with:
           name: firmware-${{ inputs.keymap }}
           if-no-files-found: ignore