Add missing bracket for Tap-Hold code sample (#9675)

The `TAPPING_TERM_PER_KEY` code sample is missing a closing bracket.
This adds it.

docs/tap_hold.md

@@ -32,6 +32,7 @@ uint16_t get_tapping_term(uint16_t keycode, keyrecord_t *record) {
             return 130;
         default:
             return TAPPING_TERM;
+    }
 }
 ```