azure-pipelines.yml: Use macOS-10.14 instead of macOS-latest to prevent PlatformNotSupported and FileNotFoundException that appear to be related to the test fixture (we get no failed tests and they complete, but the run crashes)

Author: NightOwl888

azure-pipelines.yml

@@ -480,7 +480,7 @@ stages:
           maximumAllowedFailures: 2 # Maximum allowed failures for a successful build
         macOS:
           osName: 'macOS'
-          imageName: 'macOS-latest'
+          imageName: 'macOS-10.14' # macOS-latest should not be used here because we may get OS Darwin 19.6.0, which isn't supported fully (we get PlatformNotSupportedException).
           maximumParallelJobs: 7
           maximumAllowedFailures: 2 # Maximum allowed failures for a successful build
     displayName: 'Test netcoreapp3.1,x64 on'
@@ -514,7 +514,7 @@ stages:
           maximumAllowedFailures: 2 # Maximum allowed failures for a successful build
         macOS:
           osName: 'macOS'
-          imageName: 'macOS-latest'
+          imageName: 'macOS-10.14' # macOS-latest should not be used here because we may get OS Darwin 19.6.0, which isn't supported fully (we get PlatformNotSupportedException).
           maximumParallelJobs: 7
           maximumAllowedFailures: 2 # Maximum allowed failures for a successful build
     displayName: 'Test netcoreapp3.1,x86 on'