Fix Test Failure in multi-mx in PG17

[m3hm3t]

This PR addresses a regression test failure in the multi-mx feature of Citus with the new PostgreSQL 17 version. The regression was identified during the execution of multi-node tests, specifically targeting compatibility issues introduced with PostgreSQL 17.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.65%. Comparing base (6c12b10) to head (983bd4a). Report is 1 commits behind head on naisila/pg17_support.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## naisila/pg17_support #7722 +/- ## ======================================================== + Coverage 89.61% 89.65% +0.04% ======================================================== Files 283 283 Lines 60691 60618 -73 Branches 7570 7549 -21 ======================================================== - Hits 54387 54350 -37 + Misses 4146 4113 -33 + Partials 2158 2155 -3 ```