Azure use ubuntu-latest and ubuntu-20.04

Author: scottshambaugh

azure-pipelines.yml

@@ -18,7 +18,7 @@ stages:
   jobs:
   - job: Skip
     pool:
-      vmImage: 'ubuntu-18.04'
+      vmImage: 'ubuntu-latest'
     variables:
       DECODE_PERCENTS: 'false'
       RET: 'true'
@@ -39,13 +39,13 @@ stages:
       strategy:
         matrix:
           Linux_py38:
-            vmImage: 'ubuntu-18.04'
+            vmImage: 'ubuntu-20.04'  # keep one job pinned to the oldest image
             python.version: '3.8'
           Linux_py39:
-            vmImage: 'ubuntu-18.04'
+            vmImage: 'ubuntu-latest'
             python.version: '3.9'
           Linux_py310:
-            vmImage: 'ubuntu-18.04'
+            vmImage: 'ubuntu-latest'
             python.version: '3.10'
           macOS_py38:
             vmImage: 'macOS-latest'