fix-138: Change added as a speaker email

[it-tma-tri]

This PR closes/references issue #138 It does so by changing the text as required.

How has this been tested?

Manual tested and received email as follow:

Checklist

• [x] I have added tests to cover my changes.

Summary by Sourcery

This pull request updates the email text sent to newly added speakers, enhancing the message's clarity and tone. The subject line and body of the email have been revised to provide a more welcoming and informative message.

• Bug Fixes:
  • Updated the email text for newly added speakers to improve clarity and tone.

[sourcery-ai[bot]]

Reviewer's Guide by Sourcery

This pull request addresses issue #138 by updating the email template used to invite speakers. The changes include a more welcoming greeting, a detailed and encouraging body, and a new closing line. Additionally, the email subject has been updated to be more inviting.

File-Level Changes

Files	Changes
src/pretalx/orga/views/submission.py	Updated the email template for inviting speakers to be more welcoming and informative, including changes to the greeting, body, and subject.

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[mariobehling]

Not sure why this was closed. It seems you changed the correct email, but you did not test the correct email.