Only run gitlink during Release builds

Author: AArnott

src/GitLinkTask/GitLink.props

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
-    <GitLinkEnabled Condition=" '$(DesignTimeBuild)' != 'true' ">true</GitLinkEnabled>
+    <GitLinkEnabled Condition=" '$(DesignTimeBuild)' != 'true' and '$(Configuration)' == 'Release' and '$(GitLinkEnabled)' == '' ">true</GitLinkEnabled>
     <GitLinkContinueOnError>true</GitLinkContinueOnError>
   </PropertyGroup>
 </Project>