The installation instructions of a Maven package places the `url` child
of the `repository` node in an extra indentation level. This indentation
is unnecesary since both the `id` and `url` nodes are direct children of
the `repository` node.
This commit removes the unnecessary indentation.
Refs: https://codeberg.org/forgejo/forgejo/pulls/1534
(cherry picked from commit 82f0ddad7b)
(cherry picked from commit 905e546549)
4e58ab82b7