github/workflows: 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](https://github.com/actions/upload-artifact/compare/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>

.github/workflows/code_size.yml

@@ -66,7 +66,7 @@ jobs:
       run: echo $PR_NUMBER > pr_number
     - name: Upload diff
       if: github.event_name == 'pull_request'
-      uses: actions/upload-artifact@v6
+      uses: actions/upload-artifact@v7
       with:
         name: code-size-report
         path: |

.github/workflows/mpremote.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Build mpremote wheel
       run: cd tools/mpremote && python -m build --wheel
     - name: Archive mpremote wheel
-      uses: actions/upload-artifact@v6
+      uses: actions/upload-artifact@v7
       with:
         name: mpremote
         path: |