add refs to resources

.vsts-ci.yml

@@ -37,6 +37,21 @@ variables:
       /p:DotNetRuntimeSourceFeedKey=$(dotnetbuilds-internal-container-read-token-base64)
       /p:dotnetbuilds-internal-container-read-token-base64=$(dotnetbuilds-internal-container-read-token-base64)
 
+- ${{ if eq(variables['Build.Reason'], 'PullRequest') }}:
+  - name: VmrRef
+    value: $(System.PullRequest.TargetBranch)
+- ${{ else }}:
+  - name: VmrRef
+    value: 'refs/heads/main'
+
+resources:
+  repositories:
+    - repository: vmr
+      type: github
+      name: dotnet/dotnet
+      endpoint: dotnet
+      ref: $(VmrRef)
+
 stages:
 - stage: Build
   jobs:

eng/pipelines/vmr-sync.yml

@@ -13,6 +13,7 @@ resources:
     type: github
     name: dotnet/dotnet
     endpoint: dotnet
+    ref: $(Build.SourceBranch)
 
 parameters:
 - name: vmrBranch