Update MacOS image from 10.14 to 11 (Azure#16458)

* Update powershell-core.yml

* Update release-test.yml

Author: isra-fel

.azure-pipelines/powershell-core.yml

@@ -4,7 +4,7 @@ variables:
   LinuxName: linux
   LinuxImage: ubuntu-20.04
   MacOSName: macOS
-  MacOSImage: macOS-10.14
+  MacOSImage: macOS-11
   TestFramework: netcoreapp2.1
   TestTarget: Test
   Configuration: Debug

.azure-pipelines/release-test.yml

@@ -47,17 +47,17 @@ jobs:
 - template: util/smoke-test-steps.yml
   parameters:
     name: 'MacOS_PS6_2_4_SmokeTest'
-    vmImage: 'macOS-10.15'
+    vmImage: 'macOS-11'
     psVersion: '6.2.4'
 
 - template: util/smoke-test-steps.yml
   parameters:
     name: 'MacOS_PS7_0_3_SmokeTest'
-    vmImage: 'macOS-10.15'
+    vmImage: 'macOS-11'
     psVersion: '7.0.3'
 
 - template: util/smoke-test-steps.yml
   parameters:
     name: 'MacOS_Latest_PS_SmokeTest'
-    vmImage: 'macOS-10.15'
-    psVersion: 'latest'
+    vmImage: 'macOS-11'
+    psVersion: 'latest'