Fix #4979: latex: Incorrect escaping of curly braces in index entries

[tk0miya]

Feature or Bugfix

• Bugfix

Purpose

• see Incorrect escaping of curly braces in index entries #4979

[codecov]

Codecov Report

Merging #4987 into 1.7 will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              1.7    #4987      +/-   ##
==========================================
+ Coverage   81.99%   81.99%   +<.01%     
==========================================
  Files         282      287       +5     
  Lines       37675    38000     +325     
  Branches     5846     5900      +54     
==========================================
+ Hits        30890    31158     +268     
- Misses       5481     5528      +47     
- Partials     1304     1314      +10

Impacted Files	Coverage Δ
tests/test_build_latex.py	95.1% <100%> (ø)	⬆️
sphinx/writers/latex.py	87.33% <100%> (+0.04%)	⬆️
sphinx/builders/html.py	82.54% <0%> (-0.12%)	⬇️
sphinx/apidoc.py	0% <0%> (ø)
sphinx/errors.py	68.42% <0%> (ø)
sphinx/search/__init__.py	95.11% <0%> (ø)
sphinx/__init__.py	57.5% <0%> (ø)
sphinx/quickstart.py	0% <0%> (ø)

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[jfbu]

LGTM!

[tk0miya]

Thank you for quick reviewing :-)