Co-authored-by: Randy Döring <30527984+radoering@users.noreply.github.com>

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Co-authored-by: Randy Döring <30527984+radoering@users.noreply.github.com>

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Add a warning that PyPI will be disabled automatically in a future version of Poetry if there is at least one custom source configured with another priority than `explicit` and that it should be configured explicitly with a certain priority for forward compatibility.

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

package.category doesn't make a lot of sense in the richer world of dependency groups.

The only use that is made of the category in poetry and poetry-core is that it is written to and read back from the lockfile. But no use is made of that information.