Fixed display of html signature tags in e-mails

[Lainow]

Q	A
Bug fix?	yes
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets	#14500

When signing an email is configured with HTML text. I changed the signature to HTML text, with bold characters for example. The test email received still has the HTML tags: <b>My name</b><i>My business</i>

Before

After