TST: Revisit skipped/xfailed tests

[pllim]

SKIPPED [1] tests/test_jump_twopoint_difference.py:718: Copied, but checks nothing and is named wrong
SKIPPED [1] tests/test_jump_twopoint_difference.py:738: Copied, but checks nothing
SKIPPED [1] tests/test_jump_twopoint_difference.py:799: Fails for some reason
SKIPPED [1] tests/test_jump_twopoint_difference.py:820: Fails for some reason
XFAIL tests/test_alignment.py::test_reproject[1-2-3-4]

Sounds like something needs fixing, refactoring, or at least more investigation.

(Duplicate of spacetelescope/jwst#8241)

[melanieclarke]

See also JP-3164 and associated partially completed PR #362

[pllim]

PR #362 looks stalled?