Added missing parameter for cache-key (#187)

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: [subosito]

action.yml

@@ -44,7 +44,7 @@ runs:
   using: 'composite'
   steps:
     - id: flutter-action
-      run: $GITHUB_ACTION_PATH/setup.sh -p -c '${{ inputs.cache-path }}' -n '${{ inputs.flutter-version }}' -a '${{ inputs.architecture }}' ${{ inputs.channel }}
+      run: $GITHUB_ACTION_PATH/setup.sh -p -c '${{ inputs.cache-path }}' -k '${{ inputs.cache-key }}' -n '${{ inputs.flutter-version }}' -a '${{ inputs.architecture }}' ${{ inputs.channel }}
       shell: bash
     - if: ${{ inputs.cache == 'true' }}
       uses: actions/cache@v3