Does not install with Composer w/o warnings/errors (PHP 8)

AspectMock 4.1.1 won't install cleanly under PHP 8 with Composer:
```
$ composer update
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

Problem 1
- Root composer.json requires codeception/aspect-mock 4.1.1 -> satisfiable by codeception/aspect-mock[4.1.1].
- codeception/aspect-mock 4.1.1 requires php ^7.4 -> your php version (8.1.2) does not satisfy that requirement.
```

The only way I can get it to install without errors is to use Composer's `--ignore-platform-reqs` option.

Although there are problems with `goaop/parser-reflection` under PHP 8 (see https://github.com/goaop/framework/issues/466), I believe AM itself will work without issue under the newer PHP versions (other than the problem I reported in #201).

I believe changing this `composer.json` line would be sufficient:
```
- "php": "^7.4",
+ "php": ">=7.4",
```