github: workflow: unit_test: Add system update

When I tried to push the deploy refactor, I got the following error:

Failed to fetch http://security.ubuntu.com/ubuntu/pool/main/p/pillow/python3-pil_7.0.0-4ubuntu0.4_amd64.deb  404  Not Found

It looks like this is an update issue.

Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>

.github/workflows/unit_tests.yml

@@ -12,9 +12,13 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v2
 
+      - name: Update the system
+        run: |
+          sudo apt-get update -y
+
       - name: Install dependencies
         run: |
-          sudo apt install -y shunit2 kcov bash git \
+          sudo apt-get install -y shunit2 kcov bash git \
           python-docutils dash graphviz python3-sphinx
 
       - name: Prepare for tests