Bump actions/cache from 2.1.4 to 2.1.6

Bumps [actions/cache](https://github.com/actions/cache) from 2.1.4 to 2.1.6.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](actions/cache@v2.1.4...v2.1.6)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/main.yaml

@@ -29,7 +29,7 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
           architecture: x64
-      - uses: actions/[email protected].4
+      - uses: actions/[email protected].6
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ hashFiles('**/dev-requirements.txt') }}
@@ -56,7 +56,7 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
           architecture: x64
-      - uses: actions/[email protected].4
+      - uses: actions/[email protected].6
         with:
           path: ~/.cache/pip
           key: ${{ runner.os }}-pip-${{ hashFiles('**/dev-requirements.txt') }}