rrsync: Make perl a run-time dependency (#71344)

perl is a run-time dependency, so it should be in buildInputs rather
than nativeBuildInputs.

This has been preventing patchShebangsAuto() in fixupOutputHooks from
patching the /usr/bin/perl interpreter shebang in $out/bin/rrsync since
61bc03c0.

Resolves #71198