Add string typecheck before checking length prop on authorname

[nolledgeable]

Context

• Duplicating and improving this PR from archived javascript repo. Adds a string typecheck to authorName prop to prevent ReferenceError on length property.

Summary

This PR can be summarized in the following changelog entry:

• Adds author name type check in social previews package. Props to @goaround.

Relevant technical choices:

• Added isString type check from lodash before checking string length on author name.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Verify that the Facebook title in our Social preview still functions as intended

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:

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 other environments and needs to be tested there.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests 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.

Fixes #

[marijnyoast]

CR 👌🏻

[marijnyoast]

Acceptance 👍🏻