Let templates have plaintext as contents (fixes 2702)

[kubeden]

Description

Please describe what changes you made, and why you feel they are necessary. Make sure to include
code examples, where applicable.

I introduced an additional check template.content.textContent.trim() === '' to make sure templates are not removed if they have plaintext inside.

Corresponding issue:
#2702

Testing

Please explain how you tested this change manually, and, if applicable, what new tests you added. If
you're making a change to just the website, you can omit this section.

I ran the sample server.py code provided by the person opening the PR. I then changed the source to htmx to my localhost htmx src. I added the additional check in the if statement and refreshed a few times.

Without my change:

with plaintext:

without plaintext:

With my change:

with plaintext:

without plaintext:

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded

[kubeden]

@Telroshan sorry, I tried to rebase but unsuccessfully so I hard resetted to upstream/dev which resulted in my pull request being closed (the old one).

This only has my change.

Let me know if anything's wrong.