bug#81600: 30.2; Incorrect indentation from `C-M-q' for circular objects

See attached file.  Putting point at bob and using `C-M-q' results in
the indentation shown.  The list value being assigned to `foo' is a list
of bookmarks whose names (cars) are strings that have text property
`bmkp-full-record', whose value is the cons of which the name is the
car.

(The bug has nothing to do with bookmarks.  It's about `C-M-q''s
handling of propertized strings in lists.)

All of the bookmarks should be indented to the same level, as shown in
the second example in the file (indented manually).  All of the #1= 
occurrences should be aligned.  But with `C-M-q' they're aligned except 
for the first one, and all but the first are indented under the first.


In GNU Emacs 30.2 (build 2, x86_64-w64-mingw32) of 2025-08-14 built on
 AVALON
Windowing system distributor 'Microsoft Corp.', version 10.0.26200
System Description: Microsoft Windows 10 Home (v10.0.2009.26200.9168)

Configured using:
 'configure --with-modules --without-dbus --with-native-compilation=aot
 --without-compress-install --with-tree-sitter CFLAGS=-O2
 prefix=/g/rel/install-emacs-30.2'

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

(NATIVE_COMP present but libgccjit not available)

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252