community/libphonenumber: bump pkgrel

Rebuild after soname bump in libprotobuf (missing libprotobuf.so.21).

ERROR: unsatisfiable constraints:
  so:libprotobuf.so.21 (missing):
    required by: libphonenumber-8.10.21-r2[so:libprotobuf.so.21]

CC: @Leo, @PureTryOut