Improve error handling when trying to remove non-empty directory (#2004)

Some systems (this happened to me on Oracle Solaris) might raise
`errno.EEXIST` rather than `errno.ENOTEMPTY` when trying to remove a
non-empty directory with `os.rmdir`.

I see that similar check is already present in
https://github.com/jelmer/dulwich/blob/master/dulwich/index.py#L2366
(all added with
https://github.com/jelmer/dulwich/commit/c6ce5cc181ec2a1fb132c2b9e878d22c84ca213d),
so this isn't a new thing.

dulwich/index.py

@@ -2125,7 +2125,7 @@ def _remove_empty_parents(path: bytes, stop_at: bytes) -> None:
             # Directory doesn't exist - stop trying
             break
         except OSError as e:
-            if e.errno == errno.ENOTEMPTY:
+            if e.errno in (errno.ENOTEMPTY, errno.EEXIST):
                 # Directory not empty - stop trying
                 break
             raise
@@ -2314,7 +2314,7 @@ def _transition_to_file(
             try:
                 os.rmdir(full_path)
             except OSError as e:
-                if e.errno == errno.ENOTEMPTY:
+                if e.errno in (errno.ENOTEMPTY, errno.EEXIST):
                     raise IsADirectoryError(
                         f"Cannot replace non-empty directory with file: {full_path!r}"
                     )