[DOC] Fix rb_postponed_job_register_once typo

Co-authored-by: Dustin Brown <dbrown9@gmail.com>

NEWS.md

@@ -307,7 +307,7 @@ changelog for details of the default gems or bundled gems.
     * added: `rb_postponed_job_preregister()`
     * added: `rb_postponed_job_trigger()`
     * deprecated: `rb_postponed_job_register()` (and semantic change. see below)
-    * deprecated: `rb_postponed_job_register_once()`
+    * deprecated: `rb_postponed_job_register_one()`
   * The postponed job APIs have been changed to address some rare crashes.
     To solve the issue, we introduced new two APIs and deprecated current APIs.
     The semantics of these functions have also changed slightly; `rb_postponed_job_register`

include/ruby/debug.h

@@ -643,11 +643,11 @@ VALUE rb_tracearg_object(rb_trace_arg_t *trace_arg);
  * racing with Ruby's internal use of them. These two functions are still present,
  * but are marked as deprecated and have slightly changed semantics:
  *
- * * rb_postponed_job_register now works like rb_postponed_job_register_once i.e.
+ * * rb_postponed_job_register now works like rb_postponed_job_register_one i.e.
  *   `func` will only be executed at most one time each time Ruby checks for
  *   interrupts, no matter how many times it is registered
  * * They are also called with the last `data` to be registered, not the first
- *   (which is how rb_postponed_job_register_once previously worked)
+ *   (which is how rb_postponed_job_register_one previously worked)
  */