CI: specify BaseOS for the unknown rid build. (#86688)

Author: tmds

eng/pipelines/common/global-build-job.yml

@@ -162,6 +162,7 @@ jobs:
       - template: /eng/common/templates/steps/source-build.yml
         parameters:
           platform:
+            baseOS: ${{ parameters.baseOS }}
             buildScript: $(Build.SourcesDirectory)$(dir)build$(scriptExt)
             nonPortable: ${{ parameters.isNonPortableSourceBuild }}
             targetRID: ${{ parameters.targetRid }}

eng/pipelines/common/platform-matrix.yml

@@ -307,6 +307,7 @@ jobs:
       container: SourceBuild_centos_x64 # Run the unknown-rid build on a platform with a known RID so our RID graph tooling can automatically add it to the RID graph.
       jobParameters:
         runtimeFlavor: ${{ parameters.runtimeFlavor }}
+        baseOS: linux
         buildConfig: ${{ parameters.buildConfig }}
         helixQueueGroup: ${{ parameters.helixQueueGroup }}
         isSourceBuild: true