[mono][infra] decrease CPU count for fullAOT CI build (dotnet#107531)

Author: matouskozak

eng/pipelines/common/templates/runtimes/build-runtime-tests-and-send-to-helix.yml

@@ -70,7 +70,7 @@ steps:
           displayName: "AOT compile CoreCLR tests"
           target: ${{ coalesce(parameters.llvmAotStepContainer, parameters.container) }}
       - ${{ if in(parameters.runtimeVariant, 'llvmfullaot', 'minifullaot') }}:
-        - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)MonoAot mono_fullaot ${{ parameters.buildConfig }} ${{ parameters.archType }} /p:RuntimeVariant=${{ parameters.runtimeVariant }} -maxcpucount:2
+        - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)MonoAot mono_fullaot ${{ parameters.buildConfig }} ${{ parameters.archType }} /p:RuntimeVariant=${{ parameters.runtimeVariant }} -maxcpucount:1
           displayName: "AOT compile CoreCLR tests"
           target: ${{ coalesce(parameters.llvmAotStepContainer, parameters.container) }}
     - ${{ if eq(parameters.archType, 'arm64') }}: