update branch name

Ix.NET/Source/version.json

@@ -1,7 +1,7 @@
 {
   "version": "4.2.0-preview.{height}",
   "publicReleaseRefSpec": [
-    "^refs/heads/master$", // we release out of master
+    "^refs/heads/main$", // we release out of main
     "^refs/heads/rel/v\\d+\\.\\d+", // we also release branches starting with vN.N
     "^refs/heads/rel/ix-v\\d+\\.\\d+" // we also release branches starting with vN.N
   ],

azure-pipelines.ix.yml

@@ -1,7 +1,7 @@
 trigger:
   branches:
     include:
-      - master
+      - main
       - rel/*
   paths:
     include:
@@ -12,7 +12,7 @@ trigger:
 pr:
   branches:
     include:
-      - master
+      - main
       - rel/*
   paths:
     include:
@@ -21,7 +21,7 @@ pr:
       - azure-pipelines.ix.yml
 
 pool:
-  vmImage: windows-2019
+  vmImage: windows-latest
 
 variables:
   BuildConfiguration: Release