Bump py-actions/py-dependency-install from 2 to 4 (#946)

Bumps [py-actions/py-dependency-install](https://github.com/py-actions/py-dependency-install) from 2 to 4.
- [Release notes](https://github.com/py-actions/py-dependency-install/releases)
- [Changelog](https://github.com/py-actions/py-dependency-install/blob/master/CHANGELOG.md)
- [Commits](py-actions/py-dependency-install@v2...v4)

---
updated-dependencies:
- dependency-name: py-actions/py-dependency-install
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Sam Bull <[email protected]>

.github/workflows/ci.yaml

@@ -31,7 +31,7 @@ jobs:
         restore-keys: |
             pip-lint-
     - name: Install dependencies
-      uses: py-actions/py-dependency-install@v2
+      uses: py-actions/py-dependency-install@v4
       with:
         path: requirements-dev.txt
     - name: Install itself