[dotnet] do not check OSPlatform if setting environment variable

Author: titusfortner

Diff for: dotnet/src/webdriver/SeleniumManager.cs

@@ -40,26 +40,25 @@ static SeleniumManager()
         {
             var currentDirectory = AppContext.BaseDirectory;
 
-            string file = "selenium-manager";
-            string binary = $"selenium-manager/linux/{file}";
-
             if (Environment.GetEnvironmentVariable("SE_MANAGER_PATH") != null)
             {
                 binaryFullPath = Environment.GetEnvironmentVariable("SE_MANAGER_PATH");
             }
             else if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
-                file = "selenium-manager.exe";
-                binary = $"selenium-manager/windows/{file}";
+                binaryFullPath = Path.Combine(currentDirectory, "selenium-manager\\windows\\selenium-manager.exe");
+            }
+            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+            {
+                binaryFullPath = Path.Combine(currentDirectory, "selenium-manager\\linux\\selenium-manager");
             }
             else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
             {
-                binary = $"selenium-manager/macos/{file}";
+                binaryFullPath = Path.Combine(currentDirectory, "selenium-manager\\macos\\selenium-manager");
             }
-
-            if (binaryFullPath == null)
+            else
             {
-                binaryFullPath = Path.Combine(currentDirectory, binary);
+                throw new PlatformNotSupportedException($"Selenium Manager doesn't support your runtime platform: {RuntimeInformation.OSDescription}");
             }
 
             if (!File.Exists(binaryFullPath))