Avoid context dependency in test case added by 9a71989a8.

Tom Lane <tgl@sss.pgh.pa.us>

Commit: 88824e68611a88a4ef7218c093810a94f86e12e0
Author: Tom Lane <tgl@sss.pgh.pa.us>
Date: 2025-09-12T22:45:06Z
Avoid context dependency in test case added by 9a71989a8.

It's not quite clear to me why this didn't show up in my local
check-world testing, but some of the buildfarm evidently runs
this test with a different database name.  Adjust the test
so that that doesn't affect the reported error messages.

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