aspect-build
Fix absolute label use in main attribute of py_test
In rules_python you can specify a file from another package like:
main = "//path/to:file.py",
This didn't work in rules_py since it was taking the main as a string to manipulate. This appears closer to me to the upstream logic that was mirrored, so maybe this was changed for another reason
related to https://github.com/aspect-build/rules_py/commit/f2240acff1976373b6da86be2e9d962f926bade9#diff-6878df526d6e39f46c6e953f0cfcc2e5b7938d5c4d2cbec0657e78c99b931239R2
Hm, remembering what I did here...
https://github.com/aspect-build/rules_py/commit/f2240acff1976373b6da86be2e9d962f926bade9#diff-6878df526d6e39f46c6e953f0cfcc2e5b7938d5c4d2cbec0657e78c99b931239R80-R81 "While marked label, it is more treated as a string"
I suspect this is a breaking change, in some cases users might already have a main value which isn't a legal label.
However this PR is green, so either we are missing some testing for the case I'm concerned about, or it's not actually possible to misuse the current string-typed attribute.
I don't really have the full context here, it was Alex who made this change, so probably he's the best person to review it.
