MAINT: change setuptools-scm version scheme

[mj-will]

The current configuration for setuptools_scm doesn't return a sensible version number. My understanding is that this is a result of having a release branch that has the v0.13.2 and v0.13.1 releases on it rather than them being in master. The current version gives:

nessai-0.13.1.dev62+gb142cc4.d20240823

After this change, the version on main would be

nessai-0.14.0.dev62+gb142cc4

and the release-0.13.x branch it returns

nessai-0.13.3.dev0+g06af460

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.60%. Comparing base (90526f3) to head (b142cc4).
Report is 109 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #420   +/-   ##
=======================================
  Coverage   93.60%   93.60%           
=======================================
  Files          69       69           
  Lines        6755     6755           
=======================================
  Hits         6323     6323           
  Misses        432      432           

Flag	Coverage Δ
unittests	93.60% <ø> (ø)

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[johnveitch]

LGTM