forms: Fix Contact_Form_Endpoint_Test::test_resend_email trying to actually send mail

[anomiex]

Closes MONOREP-289

Proposed changes:

WorDBless doesn't block attempts to send mail, and this test wasn't blocking it either.

In CI this was producing a message sh: 1: /usr/sbin/sendmail: not found while on individual machines it might actually send email if that binary exists.

Other information:

• Have you written new tests for your changes, if applicable?
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Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• CI happy?
• Check the CI logs for the sh: 1: /usr/sbin/sendmail: not found message.

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/contact-form/class-contact-form.php	913/1312 (69.59%)	-0.38%	5 💔

Full summary · PHP report · JS report

_{If appropriate, add one of these labels to override the failing coverage check: Covered by non-unit tests Use to ignore the Code coverage requirement check when E2Es or other non-unit tests cover the code Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage.}

[manzoorwanijk]

Looks fine to me