Try GitHub Actions by migrating updater-gui-tests job

The syntax is fairly close, so no actual changes were needed to
the commands that are run.

I did switch usage of `apt` to `apt-get` since the former isn't
supposed to be used in scripts.

I intentionally chose to not migrate the branch filter over to
reduce complexity given how fast and light this job is.

.circleci/config.yml

@@ -247,25 +247,6 @@ jobs:
           command: |
             cd admin; make test
 
-  updater-gui-tests:
-    docker:
-      - image: debian:bullseye
-    steps:
-      - checkout
-      - run:
-          name: Install dependencies
-          command: |
-            apt update && apt-get install -y libqt5designer5 python3-venv
-            cd journalist_gui
-            python3 -m venv .venv/ && source .venv/bin/activate
-            pip install --require-hashes -r dev-requirements.txt
-      - run:
-          name: Run tests
-          command: |
-            cd journalist_gui
-            source .venv/bin/activate
-            QT_QPA_PLATFORM=offscreen python3 test_gui.py -v
-
   static-analysis-and-no-known-cves:
     machine:
       image: ubuntu-2004:202010-01
@@ -413,15 +394,6 @@ workflows:
           context:
             - circleci-slack
           <<: *slack-fail-post-step
-      - updater-gui-tests:
-          filters:
-            branches:
-              ignore:
-                - /i18n-.*/
-                - /update-builder-.*/
-          context:
-            - circleci-slack
-          <<: *slack-fail-post-step
       - static-analysis-and-no-known-cves:
           requires:
             - lint

.github/workflows/ci.yaml

@@ -0,0 +1,23 @@
+name: CI
+on: [push, pull_request]
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  updater-gui-tests:
+    runs-on: ubuntu-latest
+    container: debian:bullseye
+    steps:
+      - uses: actions/checkout@v3
+      - name: Install dependencies
+        run: |
+          apt-get update && apt-get install -y libqt5designer5 python3-venv
+          cd journalist_gui
+          python3 -m venv .venv/ && source .venv/bin/activate
+          pip install --require-hashes -r dev-requirements.txt
+      - name: Run tests
+        run: |
+          cd journalist_gui
+          source .venv/bin/activate
+          QT_QPA_PLATFORM=offscreen python3 test_gui.py -v