Merge pull request #31592 from dotnet-maestro-bot/merge/release/3.1-t…

…o-main

[automated] Merge branch 'release/3.1' => 'main'

.azure/pipelines/ci.yml

@@ -716,7 +716,7 @@ stages:
       parameters:
         condition: ne(variables['SkipTests'], 'true')
         jobName: Linux_Test
-        jobDisplayName: "Test: Ubuntu 16.04 x64"
+        jobDisplayName: "Test: Ubuntu 18.04 x64"
         agentOs: Linux
         isTestingJob: true
         useHostedUbuntu: false
@@ -770,7 +770,7 @@ stages:
     displayName: 'Test: Linux Source Build'
     container: centos:7
     pool:
-      vmImage: 'ubuntu-16.04'
+      vmImage: 'ubuntu-18.04'
     variables:
       DotNetCoreSdkDir: $(Agent.ToolsDirectory)/dotnet
       # This isn't needed in the path because build does not need to _use_ global tools.

.azure/pipelines/jobs/default-build.yml

@@ -101,7 +101,7 @@ jobs:
         vmImage: macOS-10.15
       ${{ if eq(parameters.agentOs, 'Linux') }}:
         ${{ if eq(parameters.useHostedUbuntu, true) }}:
-          vmImage: ubuntu-16.04
+          vmImage: ubuntu-18.04
         ${{ if eq(parameters.useHostedUbuntu, false) }}:
           ${{ if eq(variables['System.TeamProject'], 'public') }}:
             name: NetCorePublic-Pool