Fix crossgen2 instruction set argument format (use space instead of colon)

Co-authored-by: rolfbjarne <249268+rolfbjarne@users.noreply.github.com>

Author: Copilot

dotnet/targets/Microsoft.Sdk.R2R.targets

@@ -21,8 +21,8 @@
 
 		<PropertyGroup Condition="'$(_ComputedInstructionSet)' != ''">
 			<!-- Append the instruction set to the existing PublishReadyToRunCrossgen2ExtraArgs -->
-			<PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunCrossgen2ExtraArgs)' == ''">--instruction-set:$(_ComputedInstructionSet)</PublishReadyToRunCrossgen2ExtraArgs>
-			<PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunCrossgen2ExtraArgs)' != ''">$(PublishReadyToRunCrossgen2ExtraArgs) --instruction-set:$(_ComputedInstructionSet)</PublishReadyToRunCrossgen2ExtraArgs>
+			<PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunCrossgen2ExtraArgs)' == ''">--instruction-set $(_ComputedInstructionSet)</PublishReadyToRunCrossgen2ExtraArgs>
+			<PublishReadyToRunCrossgen2ExtraArgs Condition="'$(PublishReadyToRunCrossgen2ExtraArgs)' != ''">$(PublishReadyToRunCrossgen2ExtraArgs) --instruction-set $(_ComputedInstructionSet)</PublishReadyToRunCrossgen2ExtraArgs>
 		</PropertyGroup>
 	</Target>