Fix build artifact upload (wpilibsuite#745)

Files/directories starting with . are now considered "hidden" and won't be uploaded by default. Uploading only the repository makes it so .m2 isn't in the recursive glob, and ensures settings.xml doesn't get uploaded (good practice since it can potentially contain repository credentials).

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
     - uses: actions/upload-artifact@v4
       with:
         name: Maven
-        path: ~/.m2/
+        path: ~/.m2/repository/
 
   test_examples:
     needs: build