PR Summary

Collections set_offset was coercing to float, which ruins any units we want to do. Closes #21803

Needs tests....

Tested with

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 10)
y = np.sin(x)
d = x * np.timedelta64(24, 'h') + np.datetime64('2021-11-29')

sc = plt.scatter(d, y) # showsw a plot
sc.set_offsets(list(zip(d, y)))
plt.show()

PR Checklist

Tests and Styling

• Has pytest style unit tests (and pytest passes).
• Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

• New features are documented, with examples if plot related.
• New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
• Documentation is sphinx and numpydoc compliant (the docs should build without error).