Fix a grammatical issue in String::isNotBlank docs

"except of ..." is wrong.
Instead, it should be either of the following:
  - "except ..."
  - "except for ..."
  - "with the exception of ..."

See https://www.merriam-webster.com/dictionary/except%20for
and https://ell.stackexchange.com/q/148197

libraries/stdlib/src/kotlin/text/Strings.kt

@@ -308,7 +308,7 @@ public inline fun CharSequence.isNotEmpty(): Boolean = length > 0
 
 
 /**
- * Returns `true` if this char sequence is not empty and contains some characters except of whitespace characters.
+ * Returns `true` if this char sequence is not empty and contains some characters except whitespace characters.
  *
  * @sample samples.text.Strings.stringIsNotBlank
  */
@@ -1483,4 +1483,4 @@ public fun String.toBooleanStrictOrNull(): Boolean? = when (this) {
     "true" -> true
     "false" -> false
     else -> null
-}
+}