[release/10.0] Suppress NuGet vulnerability audit warnings in RepoTasks (#66424)

* Suppress NuGet vulnerability audit warnings in RepoTasks

RepoTasks is a build-time MSBuild task project that is not shipped to
customers. Suppress NU1901-NU1904 vulnerability audit warnings to
unblock the internal CI pipeline, which has been 100% broken for 24+
hours due to a newly published advisory for the transitive dependency
System.Security.Cryptography.Xml 8.0.0.

Affects main, release/10.0, and internal/release/10.0-nonstable.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Update RepoTasks.csproj

---------

Co-authored-by: wigodbe <wigodbe@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

eng/tools/RepoTasks/RepoTasks.csproj

@@ -13,6 +13,8 @@
     <TargetLatestDotNetRuntime>false</TargetLatestDotNetRuntime>
     <!-- No need to track public APIs of these MSBuild tasks. -->
     <AddPublicApiAnalyzers>false</AddPublicApiAnalyzers>
+    <!-- Keep NuGet vulnerability audit warnings visible for transitive dependencies in this build-time tool without failing the build. -->
+    <WarningsNotAsErrors>$(WarningsNotAsErrors);NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors>
   </PropertyGroup>
 
   <ItemGroup>