fix CI actions/cache versions

Author: dpad85

.github/workflows/testnet-build.yml

@@ -45,14 +45,14 @@ jobs:
     # 2 - setup cache/jdk
 
     - name: Cache maven dependencies
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.m2
         key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
         restore-keys: ${{ runner.os }}-m2
 
     - name: Cached Konan
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.konan
         key: ${{ runner.os }}-konan-${{ hashFiles('**/*.gradle*') }}-${{ hashFiles('**/gradle/wrapper/gradle-wrapper.properties') }}