Update .gitlab-ci.yml file

.gitlab-ci.yml

+stages:          # List of stages for jobs, and their order of execution
+  - install
+  - test
+
+installation-test-xenial:       # This job runs in the build stage, which runs first.
+  stage: install
+  image: ubuntu:16.04
+  script:
+    - apt install expect -y
+    - ./auto_script_wolf
+
+installation-test-bionic:       # This job runs in the build stage, which runs first.
+  stage: install
+  image: ubuntu:18.04
+  script:
+    - apt install expect -y
+    - ./auto_script_wolf
+
+installation-test-focal:       # This job runs in the build stage, which runs first.
+  stage: install
+  image: ubuntu:20.04
+  script:
+    - apt install expect -y
+    - ./auto_script_wolf
+
+lint-test-job:   # This job also runs in the test stage.
+  stage: test    # It can run at the same time as unit-test-job (in parallel).
+  script:
+    - echo "Linting code... This will take about 10 seconds."
+    - sleep 10
+    - echo "No lint issues found."
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