Allow chmod failures on cache write

[MGatner]

Description
Cache's FileHandler will attempt to se the file mode after writes using chmod(). This is already allowed to fail (i.e. return false) since files can be writable but not owned, however some circumstances can actually cause a fatal error:

chmod(): Operation not permitted
at SYSTEMPATH/Cache/Handlers/FileHandler.php:127

Backtrace:
  1    [internal function]
       CodeIgniter\Debug\Exceptions()->errorHandler()

  2    SYSTEMPATH/Cache/Handlers/FileHandler.php:127
       chmod()

This PR catches any throwable and log and ignores the exception.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• n/a User guide updated
• Conforms to style guide