fix(manager/composer): respect the PHP override in composer.json

[internalsystemerror]

Changes:

This ensures that renovate respects the PHP override set in composer.json: https://getcomposer.org/doc/06-config.md#platform.

Given the following:

{
    "config": {
        "platform": {
            "php": "7.4.27"
        }
    },
    "require": {
        "php": "^7.4 || ~8.0.0"
    }
}

Then the detected PHP version used for composer should be 7.4.27. This PR adds that awareness to renovate.

Context:

There are several issues related which should be closed by this (for instance #4396). And mainly came about after this discussion #13637.

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please tick one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[viceice]

Otherwise LGTM

[internalsystemerror]

I will be able to fix this and finish this off tonight

[internalsystemerror]

Never mind, that was a quick fix. Sorry I'd missed this on the initial upload so I was able to push it now.

[internalsystemerror]

@rarkins @viceice Thank you both for your help with this!

[renovate-release]

🎉 This PR is included in version 31.38.2 🎉

The release is available on:

• GitHub release
• 31.38.2

Your semantic-release bot 📦🚀