Changed Warnings as Errors Settings

Author: michaelstaib

src/Directory.Build.props

@@ -11,11 +11,15 @@
     <NuGetAuditMode>direct</NuGetAuditMode>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(CI)' == 'true'">
+  <PropertyGroup Condition="'$(TreatWarningsAsErrors)' == ''">
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <WarningsNotAsErrors>NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(TreatWarningsAsErrors)' == 'false'">
+    <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
+  </PropertyGroup>
+
   <PropertyGroup>
     <Product>Hot Chocolate</Product>
     <Authors>ChilliCream authors and contributors</Authors>