[ci] Build tests on CI only when needed

[radical]

Context:
#5739 (comment)

We currently always build tests on CI even in cases where we don't need to, for example, a codeql build. We should condition the @(ProjectsToBuild) to not include the tests, maybe when $(Test)==false.

aspire/eng/Build.props

Lines 2 to 8 in a8b0bed

	<ItemGroup Condition="'$(DotNetBuildFromSource)' != 'true' and '$(DotNetBuild)' != 'true'">
	<ProjectToBuild Include="$(RepoRoot)src\**\*.csproj" Exclude="$(RepoRoot)src\Aspire.ProjectTemplates\templates\**\*.csproj" />
	<ProjectToBuild Include="$(RepoRoot)eng\dcppack\**\*.csproj" />
	<ProjectToBuild Include="$(RepoRoot)eng\dashboardpack\**\*.csproj" />
	<ProjectToBuild Include="$(RepoRoot)playground\**\*.csproj" />
	<ProjectToBuild Include="$(RepoRoot)tests\**\*.csproj" />
	</ItemGroup>

cc @eerhardt