Account Notification Settings Input Issues (UI only) (#82642)

False as a value in dropdown was causing unexpected behaviour

<!-- Describe your PR here. -->
Solves this issue : #82508

Changed checks, The setting "Off" was internally represented with the
value False, but the front-end logic did not properly handle this case.

Earlier : When selected value is Off text field shows "--"
![Screenshot 2024-12-29 at 5 13
46 PM](https://github.com/user-attachments/assets/634e1a55-aa36-4cee-9752-2192a7658440)
![Screenshot 2024-12-29 at 5 13
14 PM](https://github.com/user-attachments/assets/e7bccd89-acb3-4c16-b065-65d444de068d)


After Change
![Screenshot 2024-12-29 at 5 00
43 PM](https://github.com/user-attachments/assets/ecb81db1-d801-4207-aff1-199ee09462fc)

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static/app/components/forms/fields/selectField.tsx

@@ -120,7 +120,8 @@ export default class SelectField<OptionType extends SelectValue<any>> extends Co
           placeholder,
           ...props
         }) => {
-          const showTempNoneOption = !multiple && !props.value;
+          const showTempNoneOption =
+            !multiple && (props.value === undefined || props.value === null);
 
           return (
             <Tooltip title={disabledReason} disabled={!disabled}>