Do not use Tick.label

[lldelisle]

To support matplotlib 3.8.0:
https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.8.0.html#unused-methods-in-axis-tick-xaxis-and-yaxis

This was spotted by the galaxy tool:
https://github.com/deeptools/deepTools/actions/runs/6305763719/job/17120046090?pr=1257

Job in error state.. tool_id: deeptools_plot_correlation, exit_code: 1, stderr: Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/test_and_build/bin/plotCorrelation", line 8, in <module>
    sys.exit(main())
  File "/usr/share/miniconda3/envs/test_and_build/lib/python3.10/site-packages/deeptools/plotCorrelation.py", line 244, in main
    corr.plot_scatter(args.plotFile,
  File "/usr/share/miniconda3/envs/test_and_build/lib/python3.10/site-packages/deeptools/correlation.py", line 507, in plot_scatter
    tick.label.set_rotation(45)
AttributeError: 'XTick' object has no attribute 'label'. Did you mean: '_label'?
.

[lldelisle]

Relative to Matplotlib versions:
This commit: ce327bc
Broke compatibility with matplotlib prior to 3.5. I think it should be fixed or the pyproject should be updated.

[WardDeb]

Thanks @lldelisle this slipped under the radar, I'll make another PR to cap mpl to 3.5 or greater.