ci: use actions/cache@v3 in tests workflow

Author: Slotos

.github/workflows/tests.yml

@@ -40,7 +40,7 @@ jobs:
       - uses: actions/checkout@v3
       - run: date +%F > todays-date
       - name: Restore cache for today's nightly.
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: _neovim
           key: ${{ runner.os }}-x64-${{ hashFiles('todays-date') }}