Fix PortableBuild comparisons (#15306)

Author: jkoritzinsky

eng/common/core-templates/steps/source-build.yml

@@ -78,7 +78,7 @@ steps:
 
     portableBuildArgs=
     if [ '${{ parameters.platform.portableBuild }}' != '' ]; then
-      portableBuildArgs='/p:PortabelBuild=${{ parameters.platform.portableBuild }}'
+      portableBuildArgs='/p:PortableBuild=${{ parameters.platform.portableBuild }}'
     fi
 
     ${{ coalesce(parameters.platform.buildScript, './build.sh') }} --ci \

src/Microsoft.DotNet.Build.Tasks.Installers/build/installer.targets

@@ -122,7 +122,7 @@
     <InstallerRuntimeIdentifiers Condition="'$(InstallerRuntimeIdentifiers)' == ''">$(RuntimeIdentifiers)</InstallerRuntimeIdentifiers>
     <InstallerRuntimeIdentifier Condition="'$(InstallerRuntimeIdentifier)' == ''">$(RuntimeIdentifier)</InstallerRuntimeIdentifier>
     <!-- When building a non-portable build, BaseOS specifies a known (portable) RID that is a parent of the curent runtime identifier. -->
-    <InstallerRuntimeIdentifier Condition="'$(PortableBuild)' != 'true' and '$(BaseOS)' != '$(RuntimeIdentifier)'">$(BaseOS)</InstallerRuntimeIdentifier>
+    <InstallerRuntimeIdentifier Condition="'$(PortableBuild)' == 'false' and '$(BaseOS)' != '$(RuntimeIdentifier)'">$(BaseOS)</InstallerRuntimeIdentifier>
   </PropertyGroup>
 
   <Import Project="$(MSBuildThisFileDirectory)installer.singlerid.targets"