Bug in date_range with semi-open interval and freq='B'

[louis-red]

First contribution so this PR is really light.
#6673 is resolved on master, but this PR adds some tests to confirm this behavior.

[jreback]

can you rebase on master

[codecov]

Codecov Report

Merging #22095 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #22095      +/-   ##
==========================================
+ Coverage   92.06%   92.07%   +0.01%     
==========================================
  Files         170      170              
  Lines       50705    50688      -17     
==========================================
- Hits        46680    46671       -9     
+ Misses       4025     4017       -8

Flag	Coverage Δ
#multiple	90.48% <ø> (+0.01%)	⬆️
#single	42.31% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/core/tools/datetimes.py	85.07% <0%> (-0.15%)	⬇️
pandas/io/sas/sas_xport.py	90.23% <0%> (-0.05%)	⬇️
pandas/io/formats/html.py	88.81% <0%> (-0.04%)	⬇️
pandas/core/indexing.py	93.79% <0%> (-0.03%)	⬇️
pandas/core/groupby/generic.py	86.79% <0%> (-0.02%)	⬇️
pandas/core/sparse/frame.py	94.78% <0%> (-0.02%)	⬇️
pandas/core/indexes/interval.py	94.11% <0%> (-0.02%)	⬇️
pandas/core/dtypes/dtypes.py	96.03% <0%> (-0.02%)	⬇️
pandas/core/internals/blocks.py	94.45% <0%> (-0.02%)	⬇️
pandas/core/nanops.py	95.12% <0%> (-0.01%)	⬇️
... and 17 more

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[jreback]

thanks @louis-red FYI normally like to move things in a separate PR as the diff is more clear, but ok.

[louis-red]

thanks @jreback, I'm not as familiar with git as I thought I was, and so got a bit puzzled when you asked me to rebase, was planning on doing so this week-end. Anyway thanks for the information, I keep learning !