Add CentOSStream8_Offline_PreviousSourceBuiltSdk CI leg (#17131)

eng/pipelines/templates/stages/vmr-build.yml

@@ -145,6 +145,24 @@ stages:
         useMonoRuntime: false              # 🚫
         withPreviousSDK: true              # ✅
 
+    - template: ../jobs/vmr-build.yml
+      parameters:
+        # Changing the build name requires updating the referenced name in the source-build-sdk-diff-tests.yml pipeline
+        buildName: CentOSStream8_Offline_PreviousSourceBuiltSdk
+        isBuiltFromVmr: ${{ parameters.isBuiltFromVmr }}
+        vmrBranch: ${{ variables.VmrBranch }}
+        architecture: x64
+        pool:
+          name: ${{ variables.defaultPoolName }}
+          demands: ${{ variables.defaultPoolDemands }}
+        container: ${{ parameters.centOSStream8Container }}
+        buildFromArchive: false            # 🚫
+        enablePoison: false                # 🚫
+        excludeOmniSharpTests: true        # ✅
+        runOnline: false                   # 🚫
+        useMonoRuntime: false              # 🚫
+        withPreviousSDK: true              # ✅
+
     - template: ../jobs/vmr-build.yml
       parameters:
         # Changing the build name requires updating the referenced name in the source-build-sdk-diff-tests.yml pipeline