chore: Fix relative path to spec (in this release, regression from #515)

[dbanty]

FYI @tardyp the generator crashed when running against a spec that was a relative path 😬. Don't know why e2e tests didn't catch that, using the Path constructors there must make them absolute paths.

[codecov]

Codecov Report

Merging #517 (e78de23) into main (6e9d81f) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #517   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           48        48           
  Lines         1636      1636           
=========================================
  Hits          1636      1636           

Impacted Files	Coverage Δ
openapi_python_client/__init__.py	100.00% <100.00%> (ø)

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