minor #14579 Enhancement: Use actions/cache v2 (OskarStark)

This PR was merged into the 4.4 branch.

Discussion
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Enhancement: Use actions/cache v2

cc @smoench

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Commits
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92477a8 Enhancement: Use actions/cache v2

Author: OskarStark

.github/workflows/ci.yaml

@@ -98,7 +98,7 @@ jobs:
                 id: extract_base_branch
 
             -   name: "Cache DOCtor-RST"
-                uses: actions/cache@v1
+                uses: actions/cache@v2
                 with:
                     path: .cache
                     key: ${{ runner.os }}-doctor-rst-${{ steps.extract_base_branch.outputs.branch }}