bug#70796: 30.0.50; bug-reference-mode leading to constant GCing

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

This is in an Emacs compiled from the branch scratch/igc, but I see the
same in master.

When loading admin/igc.org in scratch/igc I see very frequent GC, even
while doing nothing at all. Memory profiler shows this

  4,192,076,326  68% - redisplay_internal (C function)
  2,997,520,400  48%  - jit-lock-function
  2,997,520,400  48%   - jit-lock-fontify-now
  2,982,457,616  48%    - jit-lock--run-functions
  2,982,457,616  48%     - run-hook-wrapped
  2,982,457,616  48%      - #<compiled-function 8A7>
  2,769,181,376  45%       - font-lock-fontify-region
  2,769,181,376  45%        - font-lock-default-fontify-region
  2,707,362,176  44%         - font-lock-fontify-keywords-region
    276,400,512   4%          + org-do-emphasis-faces
    197,821,440   3%          + org-fontify-drawers
    197,821,440   3%          + org-activate-links
    197,821,440   3%          + org-activate-tags
    197,821,440   3%          + org-activate-dates
    197,821,440   3%          + org-activate-footnote-links
    197,821,440   3%          + org-fontify-macros
    197,821,440   3%          + org-font-lock-add-priority-faces
    197,821,440   3%          + org-do-latex-and-related
    197,821,440   3%          + org-activate-code
    197,821,440   3%          + org-fontify-meta-lines-and-blocks
    197,821,440   3%          + org-fontify-inline-src-blocks
    197,821,440   3%          + org-cite-activate
     57,104,384   0%            re-search-forward
     61,819,200   1%         + font-lock-unfontify-region
    213,276,240   3%       + bug-reference-fontify
     15,062,784   0%    - run-with-timer
     15,062,784   0%     + apply
         97,280   0%  + file-remote-p
            336   0%  + desktop-auto-save-set-timer
            144   0%  + tab-bar-make-keymap
  1,955,072,562  31% + command-execute
        129,456   0% + timer-event-handler
          1,024   0% + corfu--auto-post-command
              0   0%   ...

Disabling bug-reference-mode in the Org buffer makes it stop constantly
GCing.

In GNU Emacs 30.0.50 (build 4, aarch64-apple-darwin23.4.0, NS
 appkit-2487.50 Version 14.4.1 (Build 23E224)) of 2024-05-06 built on
 pro2.fritz.box
Repository revision: 5067d5484f80ac39d9aa57bd53343e335b744003
Repository branch: scratch/igc
Windowing system distributor 'Apple', version 10.3.2487
System Description:  macOS 14.4.1


Configured using:
 'configure --cache-file
 /var/folders/1d/k_6t25f94sl83szqbf8gpkrh0000gn/T//config.cache.igc
 --with-native-compilation=no --with-mps=yes CC=clang'