Server-side base backup: why superuser, not pg_write_server_files?

Applying: Fix non-superuser server-side basebackup test on Windows
Using index info to reconstruct a base tree...
M	src/bin/pg_basebackup/t/010_pg_basebackup.pl
Falling back to patching base and 3-way merge...
Auto-merging src/bin/pg_basebackup/t/010_pg_basebackup.pl
CONFLICT (content): Merge conflict in src/bin/pg_basebackup/t/010_pg_basebackup.pl
Patch failed at 0001 Fix non-superuser server-side basebackup test on Windows

error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config advice.mergeConflict false"