Fix pagination in install-plugins.php to work with the filter install_plugins_table_api_args_$tab

[brasofilo]

We can modify the per_page value in different tabs of the Install Plugins screen using the hook install_plugins_table_api_args_$tab, but pagination does not reflect that.

Per page is add as an argument value in line 63

$args = array( 'page' => $paged, 'per_page' => $per_page );

The filter is applied on the arguments in line 118, but right after, in 132, the pagination args refer back to $per_page instead of $args['per_page'], which would produce the desired effect.

[brasofilo]

Per page in wp-admin/includes/class-wp-plugin-install-list-table.php

[ericlewis]

Yep. Patch looks good.

Removing the definition of $per_page = 30; as well would clean up the code here, though that might be unnecessary refactoring.

[mordauk]

Patch looks good to me.

[SergeyBiryukov]

In 27221:

Use filtered per_page value in WP_Plugin_Install_List_Table and WP_Theme_Install_List_Table.

props brasofilo.
fixes #25675.