backupccl: correctly handle PL/pgSQL routines during restore

This patch adds a switch on the routine language before replacements are
made in the body of a UDF or stored procedure. This avoids syntax errors
due to incorrectly using the SQL parser on a PL/pgSQL routine during
RESTORE.

Fixes cockroachdb#116480

Release note (bug fix): Fixed a bug that would cause syntax errors when
attempting to RESTORE a database with PL/pgSQL UDFs or stored procedures.
This bug only affected alpha and beta versions of 23.2.