Prevent default when the submit button is clicked while isPending is true

[sookmax]

Closes #6197

I could've placed the logic in disablePendingProps, but thought it might be confusing for the user to see the warning message every time they click on the button while pending.

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

Story

http://localhost:9003/?path=/story/button--pending-spinner&providerSwitcher-express=false&strict=true

form_submit_1080.mov

🧢 Your Project:

[snowystinger]

Thanks for the PR!

[snowystinger]

GET_BUILD

[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-canary
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

## API Changes

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