[4.4] Fix output buffering

[iRedds]

Description
Fixes #7493

Work with output buffering was carried out incorrectly.

To bypass an existing bug in tests, a hack was used

CodeIgniter4/tests/system/CodeIgniterTest.php

Lines 57 to 59 in 3b3cfb5

	if (ob_get_level() > 1) {
	ob_end_clean();
	}

In my opinion, this PR correctly completes output buffering, including for exceptions.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[iRedds]

Error installing Imagic. Tests are not available.

[michalsn]

That is a really good find and improvement. Thanks!

I have tested it a bit and see no issues.

[kenjis]

@iRedds Thank you. This made CodeIgniter.php code cleaner.