Fix GitHub Actions failure due to duplicate functions

[t-hamano]

What?

This PR checks for redeclarations in the wp_add_global_styles_for_blocks function and resolves Fatal errors in gitHub Actions.
In some actions, the following Fatal Error occurs:

Fatal error: Cannot redeclare wp_add_global_styles_for_blocks() (previously declared in /var/www/html/wp-includes/global-styles-and-settings.php:202) in /var/www/html/wp-content/plugins/plugin/lib/compat/wordpress-6.1/get-global-styles-and-settings.php on line 11

Why?

A backport was done on Changeset 54118 in WordPress core and wp_add_global_styles_for_blocks was added.
I believe this problem occurred because the function is not checked on the Gutenberg.

How?

I followed this best practice and added checks by function_exists.

Testing Instructions

In this PR, confirm that all tests pass.
Confrim that all tests pass, except for the performance test where trunk is used.

[amustaque97]

I'm not sure but the Performance Tests/Run performance tests stage is failing because of the same reason. failure link: https://github.com/WordPress/gutenberg/runs/8285679201?check_suite_focus=true#step:5:60

Could you please check it again?

Thank you

[t-hamano]

My understanding is that the performance test will not pass the test unless it is merged because trunk is also used.

[amustaque97]

I tested your changes locally (I tried in my fork version but it was a bit complex on Github so I left it there 😅 ). Performance test step doesn't throw any re-declaration exceptions now. ➕ 🚀

[andrewserong]

Thanks for looking into a fix @t-hamano! For this function, I'm wondering if instead we should be using a gutenberg prefixed version instead of attempting to use the version that's just been merged into core?

[andrewserong]

Instead of checking whether or not the core wp_add_global_styles_for_blocks exists, should we instead rename the function to gutenberg_add_global_styles_for_blocks so that in the plugin, we're always calling the Gutenberg version? This would make it similar to the function lower down in this file (gutenberg_get_global_stylesheet).

[andrewserong]

This check appears to call the function only if it doesn't exist.

Instead, should we use a gutenberg prefixed version of the function?

[t-hamano]

Thanks for the review, @andrewserong !
I have made the change to use the gutenberg_ prefix.

[andrewserong]

Thanks for following up @t-hamano, this looks good to me, and styles appear to be output correctly on my test site.

Now we just need someone with access to merge this in 😄

[andrewserong]

Thanks for merging, @noisysocks! 🙇

[ockham]

Thank you for addressing, @t-hamano and @andrewserong!

Here's some more discussion on the issue: WordPress/wordpress-develop#3206 (comment)

[ockham]

I'm going to release GB 14.0.3 in a bit to include this fix, in order to make it possible to run GB stable against Core trunk.