upgrade actions/cache version from 2 to 4 (#107)

Author: alex-ozdemir

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
         with-documentation: false
 
     - name: Setup ccache cache
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ccache-dir
         key: cvc5-pythonic-api-ccache-${{ github.sha }}
@@ -47,7 +47,7 @@ jobs:
         ccache -z
 
     - name: Setup dependencies cache
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: cvc5/build/deps
         key: cvc5-pythonic-api-deps-${{ hashFiles('cvc5/cmake/**') }}-${{ hashFiles('.github/**') }}