Ty to fix YunoHost apps package linter CI config

.github/workflows/package_linter.yml

@@ -14,10 +14,19 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - uses: actions/cache@v2
+        with:
+          path: ~/.cache/
+          key: dot-cache-files
+
       - name: 'Clone YunoHost apps package linter'
         run: |
           git clone --depth=1 https://github.com/YunoHost/package_linter ~/package_linter
 
+      - name: 'Install requirements'
+        run: |
+          pip3 install toml
+
       - name: 'Run linter'
         run: |
           ~/package_linter/package_linter.py .