Fix erroneous comment in tokenizer.cs (#12206)

The BigInteger NumberSuffixFlags enum is 'N', not 'I'. Fix the comment to indicate it as such.

src/System.Management.Automation/engine/parser/tokenizer.cs

@@ -543,7 +543,7 @@ namespace System.Management.Automation.Language
         Decimal = 0x10,
 
         /// <summary>
-        /// Indicates 'I' suffix for BigInteger (arbitrarily large integer) numerals.
+        /// Indicates 'N' suffix for BigInteger (arbitrarily large integer) numerals.
         /// </summary>
         BigInteger = 0x20
     }