Upgrade GitHub Workflow to use latest Ubuntu (#3527)

Update image label to ubuntu-latest.
Fix actions/runner-images#6002 to ensure continued support.

.github/workflows/compatibility-test.yml

@@ -5,7 +5,7 @@ on: pull_request
 jobs:
   compatibility_test:
     # https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idruns-on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     env:
       PKG_USERNAME: ${{ secrets.pkg_username }}

.github/workflows/injection-framework-test.yml

@@ -5,7 +5,7 @@ on: pull_request
 jobs:
   injection_framework_test:
     # https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idruns-on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     env:
       PKG_USERNAME: ${{ secrets.pkg_username }}

.github/workflows/integration-test.yml

@@ -5,7 +5,7 @@ on: pull_request
 jobs:
   integration_test:
     # https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idruns-on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/unit-test.yml

@@ -5,7 +5,7 @@ on: pull_request
 jobs:
   unit_test:
     # https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idruns-on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v2

.github/workflows/universe-test.yml

@@ -5,7 +5,7 @@ on: pull_request
 jobs:
   universe_test:
     # https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-syntax-for-github-actions#jobsjob_idruns-on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v2