Update various branch references to main branch (#10913)

.github/workflows/ci.yml

@@ -3,11 +3,11 @@ name: CI
 on:
   push:
     branches:
-      - master
+      - main
       - release/*
   pull_request:
     branches:
-      - master
+      - main
       - release/*
 
 jobs:

.github/workflows/on-issue-open.yml

@@ -11,7 +11,7 @@ jobs:
         uses: actions/checkout@v2
         with:
           repository: 'microsoft/azuredatastudio'
-          ref: master
+          ref: main
           path: ./actions
       - name: Install Actions
         run: npm install --production --prefix ./actions/build/actions

.github/workflows/on-pr-open.yml

@@ -12,7 +12,7 @@ jobs:
         uses: actions/checkout@v2
         with:
           repository: 'microsoft/azuredatastudio'
-          ref: master
+          ref: main
           path: ./actions
       - name: Install Actions
         run: npm install --production --prefix ./actions/build/actions