MDEV-23839 innodb_fast_shutdown=0 hang on change buffer merge

ibuf_merge_or_delete_for_page(): Do not attempt to invoke
ibuf_delete_recs() on a page of the change buffer itself.
The caller could already be holding ibuf->index->lock,
and an attempt to acquire it in S mode would hang the release server
or cause an assertion failure in rw_lock_s_lock_func() in a debug
server.

This problem was reproducible on 1 out of 2 runs of the following:
./mtr --no-reorder \
innodb.innodb-page_compression_default \
innodb.innodb-page_compression_snappy \
innodb.innodb-page_compression_zip \
innodb.innodb_wl6326_big innodb.xa_recovery

storage/innobase/ibuf/ibuf0ibuf.cc

@@ -4472,7 +4472,10 @@ ibuf_merge_or_delete_for_page(
 
 				fil_space_release(space);
 				if (UNIV_UNLIKELY(srv_shutdown_state)
-				    && !srv_fast_shutdown) {
+				    && !srv_fast_shutdown
+				    && (!block
+					|| btr_page_get_index_id(block->frame)
+					!= DICT_IBUF_ID_MIN + IBUF_SPACE_ID)) {
 					/* Prevent an infinite loop on slow
 					shutdown, in case the bitmap bits are
 					wrongly clear even though buffered