refactor: update minimum CI4 version to 4.3.5

[kenjis]

Description
CI 4.4 is already released, and there are vulnerabilities in prior to 4.3.5.

• update minimum CI4 version to 4.3.5
• remove code for CI 4.2.x or before

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

[datamweb]

I'm on mobile, but I guess we need a refactor. For example below:

shield/tests/Commands/SetupTest.php

Line 25 in 09a7cf3

if (version_compare(CodeIgniter::CI_VERSION, '4.3.0', '>=')) {

[kenjis]

Removed code for CI 4.2.x or before.

[datamweb]

LGTM!
Thank you!