Prevent CRLF conversion of inputs in json_parser test module
Do this by opening the file in PG_BINARY_R mode. This prevents us from
getting wrong byte count from stat().
Per complaint from Andres Freund
Discussion: https://postgr.es/m/
20240707052030.r77hbdkid3mwksop@awork3.anarazel.de
Backpatch to rlease 17 where this code was introduced