Revert "chore: Update github action cache to v4"

This reverts commit 00f1044.

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@v4
+      - uses: actions/cache@v2
         with:
           path: |
             ~/.m2/repository