Avoid GitHub step summary file write conflicts

Refactor coverage report for GitHub step summary to try and resolve file conflict issues (and make the code more readable).
Contributes to domaindrivendev#2836.

Directory.Build.targets

@@ -17,11 +17,21 @@
     <ReportGeneratorReportTypes Condition=" '$(ReportGeneratorOutputMarkdown)' == 'true' ">$(ReportGeneratorReportTypes);MarkdownSummaryGitHub</ReportGeneratorReportTypes>
     <ReportGeneratorTargetDirectory>$([System.IO.Path]::Combine($(ArtifactsPath), 'coverage'))</ReportGeneratorTargetDirectory>
     <MergeWith>$([System.IO.Path]::Combine($(ReportGeneratorTargetDirectory), 'coverage.json'))</MergeWith>
-    <_MarkdownSummaryPrefix>&lt;details&gt;&lt;summary&gt;:chart_with_upwards_trend: &lt;b&gt;$(AssemblyName) Code Coverage report&lt;/b&gt;&lt;/summary&gt;</_MarkdownSummaryPrefix>
-    <_MarkdownSummarySuffix>&lt;/details&gt;</_MarkdownSummarySuffix>
   </PropertyGroup>
   <Target Name="GenerateCoverageReports" AfterTargets="GenerateCoverageResultAfterTest" Condition=" '$(CollectCoverage)' == 'true' ">
     <ReportGenerator ReportFiles="@(CoverletReport)" ReportTypes="$(ReportGeneratorReportTypes)" Tag="$(Version)" TargetDirectory="$(ReportGeneratorTargetDirectory)" Title="$(AssemblyName)" VerbosityLevel="Warning" />
-    <Exec Condition=" '$(ReportGeneratorOutputMarkdown)' == 'true' " Command="pwsh -Command %22('$(_MarkdownSummaryPrefix)' + [System.Environment]::NewLine + [System.Environment]::NewLine + (Get-Content $([System.IO.Path]::Combine($(ReportGeneratorTargetDirectory), 'SummaryGithub.md')) | Out-String) + [System.Environment]::NewLine + [System.Environment]::NewLine + '$(_MarkdownSummarySuffix)') >> $(GITHUB_STEP_SUMMARY)%22" />
+    <ItemGroup>
+      <_ReportGeneratorLines Include="&lt;details&gt;&lt;summary&gt;:chart_with_upwards_trend: &lt;b&gt;$(AssemblyName) Code Coverage report&lt;/b&gt;&lt;/summary&gt;" />
+      <_ReportGeneratorLines Include="$([System.Environment]::NewLine)" />
+    </ItemGroup>
+    <ReadLinesFromFile File="$([System.IO.Path]::Combine($(ReportGeneratorTargetDirectory), 'SummaryGithub.md'))" >
+      <Output TaskParameter="Lines" ItemName="_CoverageGitHubSummary"/>
+    </ReadLinesFromFile>
+    <ItemGroup>
+      <_ReportGeneratorLines Include="@(_CoverageGitHubSummary)" />
+      <_ReportGeneratorLines Include="$([System.Environment]::NewLine)" />
+      <_ReportGeneratorLines Include="&lt;/details&gt;" />
+    </ItemGroup>
+    <WriteLinesToFile Condition=" '$(ReportGeneratorOutputMarkdown)' == 'true' " ContinueOnError="WarnAndContinue" File="$(GITHUB_STEP_SUMMARY)" Lines="@(_ReportGeneratorLines)" />
   </Target>
 </Project>