chore: Update github action cache to v4

v2 is no longer supported and is throwing errors in our unit tests

Author: ldetmer

.github/workflows/unit-tests.yml

@@ -23,7 +23,7 @@ jobs:
       - uses: actions/setup-java@v1
         with:
           java-version: ${{ matrix.java }}
-      - uses: actions/cache@v2
+      - uses: actions/cache@v4
         with:
           path: |
             ~/.m2/repository