update workflows to use actions/cache@v4 (#55)

* Update phpunit.yml

* use actions/cache@v4

Author: aaronm67

.github/workflows/phpunit.yml

@@ -23,7 +23,7 @@ jobs:
         echo "::set-output name=dir::$(composer config cache-files-dir)"
 
     - name: Cache Composer packages
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ${{ steps.composer-cache.outputs.dir }}
         key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}

.github/workflows/psalm.yml

@@ -19,7 +19,7 @@ jobs:
         echo "::set-output name=dir::$(composer config cache-files-dir)"
 
     - name: Cache Composer packages
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ${{ steps.composer-cache.outputs.dir }}
         key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.lock') }}