Make PlatformDetection.IsInHelix lazy (#68445)

* Make IsInHelix lazy

* Update src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs

Co-authored-by: Adeel Mujahid <[email protected]>

Co-authored-by: Adeel Mujahid <[email protected]>

Author: danmoseley

src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs

@@ -23,7 +23,8 @@ public static partial class PlatformDetection
         // do it in a way that failures don't cascade.
         //
 
-        public static readonly bool IsInHelix = Environment.GetEnvironmentVariables().Keys.Cast<string>().Where(key => key.StartsWith("HELIX")).Any();
+        private static Lazy<bool> s_IsInHelix => new Lazy<bool>(() => Environment.GetEnvironmentVariables().Keys.Cast<string>().Any(key => key.StartsWith("HELIX")));
+        public static bool IsInHelix => s_IsInHelix.Value;
 
         public static bool IsNetCore => Environment.Version.Major >= 5 || RuntimeInformation.FrameworkDescription.StartsWith(".NET Core", StringComparison.OrdinalIgnoreCase);
         public static bool IsMonoRuntime => Type.GetType("Mono.RuntimeStructs") != null;