Update RuntimeEnvironment.GetSystemVersion() (dotnet#89575)

This API is now emitting a valid version in alignment with
dotnet#28788.
---------
Co-authored-by: Stephen Toub <[email protected]>

Author: AaronRobinsonMSFT

src/libraries/System.Runtime.InteropServices/src/System/Runtime/InteropServices/RuntimeEnvironment.cs

@@ -34,6 +34,6 @@ public static string GetRuntimeDirectory()
         [Obsolete(Obsoletions.RuntimeEnvironmentMessage, DiagnosticId = Obsoletions.RuntimeEnvironmentDiagId, UrlFormat = Obsoletions.SharedUrlFormat)]
         public static object GetRuntimeInterfaceAsObject(Guid clsid, Guid riid) => throw new PlatformNotSupportedException();
 
-        public static string GetSystemVersion() => typeof(object).Assembly.ImageRuntimeVersion;
+        public static string GetSystemVersion() => $"v{Environment.Version}";
     }
 }

src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/RuntimeEnvironmentTests.cs

@@ -17,7 +17,8 @@ public void RuntimeEnvironmentRuntimeDirectory()
         [Fact]
         public void RuntimeEnvironmentSysVersion()
         {
-            Assert.NotEmpty(RuntimeEnvironment.GetSystemVersion());
+            // The historical format of this API is "vX.Y.Z", so we validate and retain that.
+            Assert.Equal($"v{Environment.Version}", RuntimeEnvironment.GetSystemVersion());
         }
 
 #pragma warning disable SYSLIB0019 // RuntimeEnvironment members SystemConfigurationFile, GetRuntimeInterfaceAsIntPtr, and GetRuntimeInterfaceAsObject are no longer supported and throw PlatformNotSupportedException.