switch github actions to run on ubuntu 22.04

the 20.04 runner was deprecated and removed:
actions/runner-images#11101

Author: waskyo

.github/workflows/run_mypy.yaml

@@ -5,7 +5,7 @@ on: [pull_request, push]
 jobs:
   run_mypy:
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
     - uses: actions/checkout@v1

.github/workflows/run_pycodestyle.yaml

@@ -5,7 +5,7 @@ on: [pull_request, push]
 jobs:
   run_pycodestyle:
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
 
     steps:
     - uses: actions/checkout@v1