[NFC] Partial backport of 0c1d533c to avoid random test fails

[demeritcowboy]

Overview

Random test fails because the url port is e.g. 5600 so the links in the email body cause the assertNotContains to fail.

This was fixed in master from #0c1d533c, so backporting that part of it since still seeing it on 5.66 PRs.

[civibot]

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[demeritcowboy]

jenkins retest this please