fixed cache@v2 to v4

Author: haggaila

.github/workflows/main.yml

@@ -51,7 +51,7 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
       - name: Pip cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-${{ matrix.python-version }}-pip-tests-${{ hashFiles('setup.py','requirements-dev.txt','constraints.txt') }}