event#32: Fix bad variable in message template

[MegaphoneJon]

Overview

There's an incorrect variable in the "Confirm Invitation" message template.

Before

Bad URL for self-service updates.

After

Good URL for self-service updates.

[civibot]

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[yashodha]

@MegaphoneJon this should be

['name' => 'participant_confirm', 'type' => 'html'],

instead of
['name' => 'participant_confirm_html', 'type' => 'html'],

[mlutfy]

edit: my bad, I misread, sorry!

[yashodha]

@MegaphoneJon Fix looks good. In upgrade this should be
['name' => 'participant_confirm', 'type' => 'html'],

instead of
['name' => 'participant_confirm_html', 'type' => 'html'],

[mlutfy]

Test fail seems unrelated:

Test Result (1 failure / +1)
    api.v4.Entity.ConformanceTest.testConformance

[mlutfy]

jenkins, test this please

[seamuslee001]

Changes look correct to me merging as per review from @yashodha