Fix checking if plugin status is not install

[westonruter]

This is a sub-PR of #1126 which is also about fixing issues that PHPStan's static analysis uncovered. In PHPStan level 4:

basic dead code checking - always false instanceof and other type checks, dead else branches, unreachable code after return; etc.

The following issues were reported in includes/admin/plugins.php:

  167    Result of || is always true.                                                                                                                       
         💡 Because the type is coming from a PHPDoc, you can turn off this check by setting treatPhpDocTypesAsCertain: false in your phpstan.neon.         
  167    Strict comparison using !== between 'install' and array{status: string, url: string, version: string, file: string} will always evaluate to true.  
         💡 Because the type is coming from a PHPDoc, you can turn off this check by setting treatPhpDocTypesAsCertain: false in your phpstan.neon.         
  189    Result of || is always true.                                                                                                                       
         💡 Because the type is coming from a PHPDoc, you can turn off this check by setting treatPhpDocTypesAsCertain: false in your phpstan.neon.         
  189    Strict comparison using !== between 'install' and array{status: string, url: string, version: string, file: string} will always evaluate to true. 

The $status variable is populated with the return value of install_plugin_install_status() which is always an array with these keys:

Therefore, the current checks for 'install' !== $status will always evaluate to false because $status is always an array and never a string.

This was introduced in #1091. We need to make sure that fixing this static analysis bug doesn't cause a regression in the expected behavior.

Again, to prevent this from happening in the future, we need to increase the PHPStan level from 0 (#775).

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Co-authored-by: westonruter <westonruter@git.wordpress.org>
Co-authored-by: mukeshpanchal27 <mukesh27@git.wordpress.org>
Co-authored-by: felixarntz <flixos90@git.wordpress.org>

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[felixarntz]

@westonruter Wow, this is a pretty severe bug (not security-wise, but UX-wise). Glad you caught this! 🎉

[westonruter]

PHPStan caught it. I'm just the messenger 😀

[mukeshpanchal27]

🚀