Update dependencies of pastas 1.6

[raoulcollenteur]

Short Description

Update deps to align with Pandas 2.1. I think it's time to not support pandas 1 anymore, since most/everyone is on 2 by now and Pandas 3, and Python 2 is coming.

For reference: https://pandas.pydata.org/pandas-docs/version/2.1/getting_started/install.html

Checklist before PR can be merged:

• closes issue Possible different in results between different versions of Python packages #749 ?
• is documented
• Format code with Ruff formatting
• type hints for functions and methods
• tests added / passed

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ ∅

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (84d1a8b)	6332	4811	75.98%
Head commit (c0b39ef)	6332 (+0)	4811 (+0)	75.98% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#769)	0	0	∅ (not applicable)

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[dbrakenhoff]

Looks good to me.