Add a NEWS entry.

Misc/NEWS.d/next/Core and Builtins/2023-06-02-15-15-41.gh-issue-104812.dfZiG5.rst

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+The "pending call" machinery now works for all interpreters, not just the
+main interpreter, and runs in all threads, not just the main thread. Some
+calls are still only done in the main thread, ergo in the main interpreter.
+This change does not affect the existing public C-API
+(``Py_AddPendingCall()``) which still only targets the main thread. The new
+functionality is meant strictly for internal use.  This change brings the
+capability in line with the intention when the state was made
+per-interpreter several years ago.