Only build the GC simulator tests in the GC simulator leg

Only build the GC simluator tests instead of all Pri1 tests. When we build all Pri1 tests in this leg, nearly all tests are skipped as only the GCSimluator tests are actually run. These skipped tests leave a ton of files on disk, causing issues in Helix. By only building the actual tests we are going to run, we can avoid this additional infrastructure cost.

eng/pipelines/common/templates/runtimes/build-test-job.yml

@@ -95,6 +95,18 @@ jobs:
         - name: runtimeFlavorArgs
           value: '-mono'
 
+      - name: testTreeFilterArg
+        value: ''
+
+      # Only build GCSimulator tests when the gc-simulator group is specified.
+      - ${{ if eq(parameters.testGroup, 'gc-simulator') }}:
+        - ${{ if eq(parameters.osGroup, 'windows') }}:
+          - name: testTreeFilterArg
+            value: '-tree GC/Scenarios/GCSimulator'
+        - ${{ if ne(parameters.osGroup, 'windows') }}:
+          - name: testTreeFilterArg
+            value: '-tree:GC/Scenarios/GCSimulator'
+
     steps:
 
     # Install test build dependencies
@@ -113,7 +125,7 @@ jobs:
         displayName: Disk Usage before Build
 
     # Build managed test components
-    - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)Managed allTargets skipnative skipgeneratelayout skiptestwrappers $(buildConfig) $(archType) $(runtimeFlavorArgs) $(crossArg) $(priorityArg) ci /p:TargetOS=AnyOS
+    - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)Managed allTargets skipnative skipgeneratelayout skiptestwrappers $(buildConfig) $(archType) $(runtimeFlavorArgs) $(crossArg) $(priorityArg) $(testTreeFilterArg) ci /p:TargetOS=AnyOS
       displayName: Build managed test components
 
     - ${{ if in(parameters.osGroup, 'OSX', 'iOS', 'tvOS') }}: