BUG: Fixed msgpack roundtrip with PeriodIndex

[TomAugspurger]

Closes #24135

[pep8speaks]

Hello @TomAugspurger! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/indexes/period.py !

• There are no PEP8 issues in the file pandas/io/packers.py !

• There are no PEP8 issues in the file pandas/tests/io/test_packers.py !

[jreback]

lgtm.

[codecov]

Codecov Report

Merging #24335 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24335      +/-   ##
==========================================
+ Coverage   92.28%   92.28%   +<.01%     
==========================================
  Files         162      162              
  Lines       51831    51833       +2     
==========================================
+ Hits        47830    47833       +3     
+ Misses       4001     4000       -1

Flag	Coverage Δ
#multiple	90.68% <100%> (ø)	⬆️
#single	43% <66.66%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/packers.py	88.08% <100%> (ø)	⬆️
pandas/core/indexes/period.py	93.09% <100%> (+0.03%)	⬆️
pandas/util/testing.py	87.58% <0%> (+0.09%)	⬆️

---

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[codecov]

Codecov Report

Merging #24335 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24335      +/-   ##
==========================================
+ Coverage   92.28%   92.28%   +<.01%     
==========================================
  Files         162      162              
  Lines       51831    51833       +2     
==========================================
+ Hits        47830    47833       +3     
+ Misses       4001     4000       -1

Flag	Coverage Δ
#multiple	90.68% <100%> (ø)	⬆️
#single	43% <66.66%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/io/packers.py	88.08% <100%> (ø)	⬆️
pandas/core/indexes/period.py	93.09% <100%> (+0.03%)	⬆️
pandas/util/testing.py	87.58% <0%> (+0.09%)	⬆️

---

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 216986d...71a7f3d. Read the comment docs.

[jreback]

thanks