Ensure apt-get update is executed in github runner

Otherwise we can't install libcurl4-openssl-dev.
See: actions/runner-images#5470

Signed-off-by: Ronan Abhamon <[email protected]>

.github/workflows/main.yml

@@ -9,6 +9,7 @@ jobs:
     - uses: actions/checkout@v2
     - name: Install dependencies
       run: |
+        sudo apt-get update
         sudo apt-get -y install nbdkit-plugin-dev libcurl4-openssl-dev
     - name: Build multi-http-plugin
       run: |