lib: Fix TypeScript error in TypeaheadSelect correctly

The "isDisabled" in the props needs to remain optional, otherwise
every user has to provide it. The default value in the function does
nothing for this.

The real problem was assigning that to MenuToggleProps, but there the
default value will make sure that isDisabled is not undefined anymore.

pkg/lib/cockpit-components-typeahead-select.tsx

@@ -130,7 +130,7 @@ export interface TypeaheadSelectProps extends Omit<SelectProps, 'toggle' | 'onSe
   /** Message to display when no options match the filter. */
   noOptionsFoundMessage?: string | ((filter: string) => string);
   /** Flag indicating the select should be disabled. */
-  isDisabled: boolean;
+  isDisabled?: boolean;
   /** Width of the toggle. */
   toggleWidth?: string;
   /** Additional props passed to the toggle. */