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.

Explicit sources are considered only for packages that explicitly indicate their source.

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