BUG: do not escape placeholder in to_latex()

[toobaz]

• closes Spurious braces in output of DataFrame.to_latex() with MultiIndex columns, MultiIndex index and missing level name #18667
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #18670 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18670      +/-   ##
==========================================
- Coverage   91.59%   91.57%   -0.02%     
==========================================
  Files         153      153              
  Lines       51212    51210       -2     
==========================================
- Hits        46908    46896      -12     
- Misses       4304     4314      +10

Flag	Coverage Δ
#multiple	89.43% <ø> (-0.01%)	⬇️
#single	40.67% <ø> (-0.11%)	⬇️

Impacted Files	Coverage Δ
pandas/io/formats/format.py	96.09% <ø> (+0.07%)	⬆️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/util/testing.py	81.82% <0%> (-0.2%)	⬇️
pandas/core/frame.py	97.81% <0%> (-0.1%)	⬇️
pandas/core/indexes/datetimes.py	95.68% <0%> (-0.01%)	⬇️

---

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[codecov]

Codecov Report

Merging #18670 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #18670      +/-   ##
==========================================
- Coverage   91.59%   91.55%   -0.04%     
==========================================
  Files         153      153              
  Lines       51212    51212              
==========================================
- Hits        46908    46888      -20     
- Misses       4304     4324      +20

Flag	Coverage Δ
#multiple	89.41% <ø> (-0.03%)	⬇️
#single	40.67% <ø> (-0.11%)	⬇️

Impacted Files	Coverage Δ
pandas/io/formats/format.py	96.09% <ø> (+0.07%)	⬆️
pandas/io/gbq.py	25% <0%> (-58.34%)	⬇️
pandas/plotting/_converter.py	63.44% <0%> (-1.82%)	⬇️
pandas/core/frame.py	97.81% <0%> (-0.1%)	⬇️

---

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[jreback]

cc @agartland
cc @syxolk
cc @MXKY

this looks reasonable, if any of you have any thoughts.

[syxolk]

I don't see the use case. @toobaz Can you give further explanations?

[toobaz]

I don't see the use case. @toobaz Can you give further explanations?

I gave an example in #18667, but maybe the following looks more "normal":

pd.DataFrame(-1,
             index=pd.MultiIndex.from_product([[1, 2]]*3, names=['a', 'b', 'c']),
             columns=range(2)
             ).unstack().to_latex()

[jreback]

thanks @toobaz