DOC: Fix rolling doc with win_type triang (#22268)

[ihsansecer]

• closes Rolling with win_type='triang' strange results #22268
• passes git diff upstream/master -u -- "*.py" | flake8 --diff

[codecov]

Codecov Report

Merging #26794 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26794      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files         178      178              
  Lines       50774    50774              
==========================================
- Hits        46579    46574       -5     
- Misses       4195     4200       +5

Flag	Coverage Δ
#multiple	90.32% <ø> (ø)	⬆️
#single	41.19% <ø> (-0.11%)	⬇️

Impacted Files	Coverage Δ
pandas/core/window.py	96.4% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.84% <0%> (-0.11%)	⬇️

---

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[codecov]

Codecov Report

Merging #26794 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #26794      +/-   ##
==========================================
- Coverage   91.73%   91.72%   -0.01%     
==========================================
  Files         178      178              
  Lines       50774    50774              
==========================================
- Hits        46579    46574       -5     
- Misses       4195     4200       +5

Flag	Coverage Δ
#multiple	90.32% <ø> (ø)	⬆️
#single	41.19% <ø> (-0.11%)	⬇️

Impacted Files	Coverage Δ
pandas/core/window.py	96.4% <ø> (ø)	⬆️
pandas/io/gbq.py	78.94% <0%> (-10.53%)	⬇️
pandas/core/frame.py	96.88% <0%> (-0.12%)	⬇️
pandas/util/testing.py	90.84% <0%> (-0.11%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b8ad9da...c2f6aa6. Read the comment docs.

[WillAyd]

Thanks!