[dotnet] Address some nullability warnings in driver options

Author: nvborisenko

dotnet/src/webdriver/Chromium/ChromiumOptions.cs

@@ -615,7 +615,7 @@ private static void AddAndroidOptions(Dictionary<string, object> chromeOptions,
 
             if (!string.IsNullOrEmpty(androidOptions.AndroidProcess))
             {
-                chromeOptions["androidProcess"] = androidOptions.AndroidProcess;
+                chromeOptions["androidProcess"] = androidOptions.AndroidProcess!;
             }
 
             if (androidOptions.UseRunningApp)

dotnet/src/webdriver/Firefox/FirefoxOptions.cs

@@ -289,7 +289,7 @@ private Dictionary<string, object> GenerateFirefoxOptionsDictionary()
 
             if (!string.IsNullOrEmpty(this.BinaryLocation))
             {
-                firefoxOptions[FirefoxBinaryCapability] = this.BinaryLocation;
+                firefoxOptions[FirefoxBinaryCapability] = this.BinaryLocation!;
             }
 
             if (this.LogLevel != FirefoxDriverLogLevel.Default)
@@ -345,12 +345,12 @@ private static void AddAndroidOptions(FirefoxAndroidOptions androidOptions, Dict
 
             if (!string.IsNullOrEmpty(androidOptions.AndroidDeviceSerial))
             {
-                firefoxOptions["androidDeviceSerial"] = androidOptions.AndroidDeviceSerial;
+                firefoxOptions["androidDeviceSerial"] = androidOptions.AndroidDeviceSerial!;
             }
 
             if (!string.IsNullOrEmpty(androidOptions.AndroidActivity))
             {
-                firefoxOptions["androidActivity"] = androidOptions.AndroidActivity;
+                firefoxOptions["androidActivity"] = androidOptions.AndroidActivity!;
             }
 
             if (androidOptions.AndroidIntentArguments.Count > 0)