 Pin codecov/codecov-action to v3.1.6

This is the only version in the v3 series to use a non-EOL NodeJS
runtime.
Ref: #74 (comment)

We can't yet upgrade to v4 due to its API changes.

Co-Authored-By: Felix Fontein <felix@fontein.de>

action.yml

@@ -673,7 +673,7 @@ runs:
       Send the coverage data over to
       https://codecov.io/gh/${{ github.repository }}
     if: steps.ansible-test-command.outputs.has-coverage == 'true'
-    uses: codecov/codecov-action@v3
+    uses: codecov/codecov-action@v3.1.6
     with:
       files: >-
         ${{