Fix: ubuntu version to 20.04

.github/workflows/black.yml

@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   lint:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
       - uses: psf/black@stable

.github/workflows/build-pypi.yml

@@ -15,7 +15,7 @@ on:
 jobs:
 
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version: ["3.7"]

.github/workflows/codeql.yml

@@ -23,7 +23,7 @@ on:
 jobs:
   analyze:
     name: Analyze
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     permissions:
       actions: read
       contents: read

.github/workflows/test.yaml

@@ -3,7 +3,7 @@ on: [push, pull_request]
 jobs:
 
   build:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version: ["3.7"]