[dotnet] Address some build warnings (#15157)

Author: nvborisenko

dotnet/src/webdriver/Cookie.cs

@@ -277,7 +277,7 @@ public static Cookie FromDictionary(Dictionary<string, object> rawCookie)
         {
             if (rawCookie == null)
             {
-                throw new ArgumentNullException(nameof(rawCookie), "Dictionary cannot be null");
+                throw new ArgumentNullException(nameof(rawCookie));
             }
 
             string name = rawCookie["name"].ToString();

dotnet/src/webdriver/CookieJar.cs

@@ -127,7 +127,7 @@ public void DeleteAllCookies()
             {
                 var rawCookie = driver.InternalExecute(DriverCommand.GetCookie, new() { { "name", name } }).Value;
 
-                return Cookie.FromDictionary((Dictionary<string, object>)rawCookie);
+                return Cookie.FromDictionary((Dictionary<string, object>)rawCookie!);
             }
             catch (NoSuchCookieException)
             {

dotnet/src/webdriver/Internal/FileUtilities.cs

@@ -188,12 +188,18 @@ public static string GetCurrentDirectory()
 
             string currentDirectory = location!;
 
+#if !NET8_0_OR_GREATER
             // If we're shadow copying, get the directory from the codebase instead
             if (AppDomain.CurrentDomain.ShadowCopyFiles)
             {
-                Uri uri = new Uri(executingAssembly.CodeBase);
-                currentDirectory = Path.GetDirectoryName(uri.LocalPath)!;
+                var codeBase = executingAssembly.CodeBase;
+
+                if (codeBase is not null)
+                {
+                    currentDirectory = Path.GetDirectoryName(codeBase);
+                }
             }
+#endif
 
             return currentDirectory;
         }