fix(jsx-email): make jsx files visible to preview app

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Component / Package Name: Preview App

This PR contains:

• [x] bugfix
• [ ] feature
• [ ] refactor
• [ ] documentation
• [ ] other

Are tests included?

• [x] yes (sort of)
• [ ] no

Breaking Changes?

• [ ] yes (breaking changes will not be merged unless absolutely necessary)
• [x] no

If yes, please include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Fixes #103

Description

This PR fixes a bug whereby the preview app wasn't "seeing" .jsx template files due to a glob not being setup for both jsx and tsx.