convert FromCommandLine to str before building Step

[braingram]

When string arguments are passed in via the command line they are converted to FromCommandLine instances. Convert them back to strings before providing them as keyword arguments while building the step.

It appears this conversion is only needed to resolve the path of input and output files provided to the step

stpipe/src/stpipe/config_parser.py

Lines 38 to 46 in 454314b

	if not isinstance(path, cmdline.FromCommandLine):
	try:
	path = str(path)
	except ValueError:
	pass
	path = os.path.join(root_dir, path)
	path = os.path.abspath(path)

This will hopefully fix the failing regression tests for spacetelescope/jwst#7403 and other instances of similar failures.

[codecov]

Codecov Report

Base: 0.00% // Head: 0.00% // No change to project coverage 👍

Coverage data is based on head (dac38ef) compared to base (454314b).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@          Coverage Diff           @@
##           master     #78   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files          25      25           
  Lines        3060    3066    +6     
======================================
- Misses       3060    3066    +6     

Impacted Files	Coverage Δ
src/stpipe/step.py	0.00% <0.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[hbushouse]

Regtest run using this PR branch shows no errors for the niriss_soss tests that previously crashed!
https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/518/
(other failures are expected, due to other mergers)

[hbushouse]

I don't know if it's the right change to make, but it seems to work!

[nden]

This looks reasonable to me. I think the problem started when list arguments were enabled again in #73.
Is it possible to come up with a test for this case?

[nden]

I tested manually running a step with list parameters and confirmed this works. Writing a formal test can be done later.