ci: use ubuntu-22.04 to support python 3.7

Author: percevalw

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ on:
 
 jobs:
   Linting:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
@@ -27,7 +27,7 @@ jobs:
         run: SKIP=no-commit-to-branch pre-commit run --all-files
 
   Pytest:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: true
       matrix:
@@ -81,7 +81,7 @@ jobs:
       coverage-branch: coverage
 
   Documentation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-python@v2
@@ -101,7 +101,7 @@ jobs:
         mkdocs build --clean
 
   Installation:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: