bug#69266: 30.0.50; bibtex-parse-entry misreads escaped \}

[Ihor Radchenko]

Consider the following bibtex entry:

@InCollection{Geyer2011,
  title           = {Introduction to Markov Chain Monte  \} Carlo},
  pages           = 45,
}

According to https://www.bibtex.org/SpecialSymbols/, characters that
conflict with Bibtex format description can be \-escaped.

In the above, with point at the beginning of the entry, M-:
(bibtex-parse-entry t), yields

("=type=" . "InCollection")
("=key=" . "Geyer2011")
("title" . "Introduction to Markov Chain Monte  \\")

The escaped \} is treated as closing }, which is incorrect.

Expected: escaping is properly processed.

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.41, cairo version 1.18.0) of 2024-02-18 built on localhost
Repository revision: 951379a0983ea66b1396d07628bb726f033ea24b
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101011
System Description: Gentoo Linux

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Ihor Radchenko // yantar92,
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