Fix quotes strings error (#100)

Bug reported
adrienverge/yamllint#663 (comment).

Sorry @p-j-smith, my bad.

actions/linting/action.yml

@@ -23,10 +23,12 @@ runs:
         path: |-
           ~/.ansible
           ~/.cache/pre-commit
-        key: \
+        # yamllint disable-line rule:quoted-strings
+        key: "\
           cache-\
           ${{ hashFiles(inputs.ansible-roles-config) }}-\
-          ${{ hashFiles(inputs.pre-commit-config) }}
+          ${{ hashFiles(inputs.pre-commit-config) }}\
+          "
       if: inputs.ansible-roles-config != 'missing'
 
     - name: Cache pre-commit