upgrade actions/cache version

Author: dhacks541

.github/workflows/test_code.yml

@@ -12,13 +12,13 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Cache pip
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.cache/pip
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
         restore-keys: ${{ runner.os }}-pip-
     - name: Cache PlatformIO
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.platformio
         key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}