Avoid duplicate empty line when converting header1 markdown to html

[cristipaval]

<h1> tags break the line anyway, there is no need to add a <br /> when converting # markdown to html. This is needed to make header1 look nicer.

Fixed Issues

https://github.com/Expensify/Expensify/issues/238874

Tests

1. What unit/integration tests cover your change? What autoQA tests cover your change?

• there are automated tests added which check that the markdown converts to html as expected.

1. What tests did you perform that validates your changes worked?

• Link the expensify-common local repository by following these steps
• Run the app
• Open any chat and send a custom subject message like following:
  # Custom subject
The message body
• Check that there is no empty lines between the header and the message body

QA

1. What does QA need to do to validate your changes?

• Run the app
• Open any chat and send a custom subject message like following:
  # Custom subject
The message body
• Check that there is no empty lines between the header and the message body

[cristipaval]

bump @joelbettner

[joelbettner]

👍 LGTM!