MNT: Drop Python 3.7 support

[effigies]

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)

Summary

• Drops Python 3.7 support

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.21 :warning:

Comparison is base (426564e) 81.77% compared to head (c9989ba) 81.56%.

:exclamation: Current head c9989ba differs from pull request most recent head 6ec7755. Consider uploading reports for the commit 6ec7755 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #669 +/- ## ========================================== - Coverage 81.77% 81.56% -0.21% ========================================== Files 20 20 Lines 4400 4400 Branches 1264 0 -1264 ========================================== - Hits 3598 3589 -9 - Misses 798 811 +13 + Partials 4 0 -4 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `81.56% <ø> (-0.21%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype#carryforward-flags-in-the-pull-request-comment) to find out more. [see 4 files with indirect coverage changes](https://app.codecov.io/gh/nipype/pydra/pull/669/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype)

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[effigies]

@mgxd Do you know where your Dockerfile is that you used to build https://hub.docker.com/r/mgxd/slurm? We need to update it with a newer Python.

[djarecka]

There is also a newer container that was found here: https://github.com/nipype/pydra/discussions/667 but I haven't had time to check why some tests are failing