Try just running PTemplates in helix

Author: wtgodbe

.azure/pipelines/ci-public.yml

@@ -582,10 +582,10 @@ stages:
                   /p:VsTestUseMSBuildOutput=false
           displayName: Build shared fx
         # -noBuildRepoTasks -noBuildNative -noBuild to avoid repeating work done in the previous step.
-        - script: ./eng/build.cmd -ci -prepareMachine -nativeToolsOnMachine -nobl -all -noBuildRepoTasks -noBuildNative -noBuild -test
+        - script: ./eng/build.cmd -ci -prepareMachine -nativeToolsOnMachine -all -noBuildRepoTasks -noBuildNative -noBuild -test
                   -projects eng\helix\helix.proj /p:IsHelixPRCheck=true /p:IsHelixJob=true
                   /p:CrossgenOutput=false /p:ASPNETCORE_TEST_LOG_DIR=artifacts/log $(_InternalRuntimeDownloadArgs)
-                  /p:VsTestUseMSBuildOutput=false
+                  /p:VsTestUseMSBuildOutput=false /p:OnlyTestProjectTemplates=true
           displayName: Run build.cmd helix target
           env:
             HelixApiAccessToken: $(HelixApiAccessToken) # Needed for internal queues

eng/helix/helix.proj

@@ -6,6 +6,7 @@
       This must be reset in order for Build.props to evaluate a list of projects to be tested on Helix.
     -->
     <ProjectToBuild Condition="'$(ProjectToBuild)' == '$(MSBuildProjectFullPath)'"/>
+    <ProjectToBuild Condition="'$(OnlyTestProjectTemplates)' == 'true'">$(RepoRoot)src\ProjectTemplates\**\*.csproj</ProjectToBuild>
 
     <!--
       Do not load NuGet.targets since this project doesn't reference anything from NuGet. Reduces `msbuild`