Add default to onDiscard in UnsavedChangesModal

[igorschoester]

Context

Summary

This PR can be summarized in the following changelog entry:

• Fixes a bug where a React prop type warning would occur in the First time configuration, due to the interface of the useBlocker hook.

Relevant technical choices:

Add default to onDiscard in UnsavedChangesModal
While not necessarily useful without, it is easier to work with like this.
Mostly because the useBlocker from react-router-dom has undefined for the reset and proceed functions unless actively blocking.
We could rewrite the usage there to force not rendering this depending on the state. But that is what the isOpen is supposed to be for already.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Enable debug output (SCRIPT_DEBUG)
• Visit Yoast > General > FTC
• Verify the warning in the browser console is no longer there

Warning: Failed prop type: The prop onDiscard is marked as required in UnsavedChangesModal, but its value is undefined.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

• Regression test going away from the FTC with unsaved changes
  • We should get the modals confirming that we want to move away from the FTC and we should also confirm that dismissing those modals works as expected.
• Regression test discarding changes in the settings page
  • We should get the modals confirming that we want to discard changes and we should also confirm that dismissing those modals works as expected.

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #21728

[igorschoester]

A bit weird because it does not throw, it logs.

This tests the original issue. That the React warning is gone when not passing onClose or onDiscard.
Try to put the isRequired back on them to see if it then fails.

[coveralls]

Pull Request Test Coverage Report for Build 04401d5eb85e3c9040ca6a99c1ca7597fcedf2b6

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 54.575%

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Totals
Change from base Build 770c2d5b44bd927478799077a816eaadc1541dcf:	0.003%
Covered Lines:	29661
Relevant Lines:	54627

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💛 - Coveralls

[pls78]

CR: ✅

[leonidasmi]

Acceptance test is ✅