fix: Memory leak with cal embed modal box

[nusr]

What does this PR do?

• Fixes Memory leak with cal embed modal box #17008

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• Are there environment variables that should be set?
• What are the minimal test data to have?
• What is expected (happy path) to have (input and output)?
• Any other important info that could help to test that PR

Checklist

• I haven't read the contributing guide
• My code doesn't follow the style guidelines of this project
• I haven't commented my code, particularly in hard-to-understand areas
• I haven't checked if my changes generate no new warnings

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[graphite-app]

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[github-actions]

E2E results are ready!

• Workflow #34470.1 latest results

[clicktodev]

I don't know is this is the proper fix because now the embed doesn't unmount when closed thus it doesn't refetch when closed and reopened.

e.g.

1. user 1 opens modal
2. user 1 selects date and time
3. user 1 closes modal
4. user 2 books the the same date
5. user 1 opens modal again after a while
6. modal doesn't fetch available dates
7. user 1 tries to book the same date again
8. user 1 gets "Could not book the meeting" error

i believe the correct approach is to unmount the component when closed