In Go commit edf006c9a3fbb23304dd53590e62fef9250ebb94 (released in Go
1.27.0), net/mail was changed to add escaping to some error messages.
In the cmd/chasquid-util/test_dkim.cmy test, we were validating output
against one of those messages, so in Go 1.27.0 the test now fails.
This patch updates the test to match the new string.
Note we don't increase the minimum version yet in go.mod: 1.27 is newly
released, and chasquid can be built fine with 1.25 for now.
We may end up increasing the minimum version later if this discrepancy
causes confusion or test errors.
Alberto Bertogli