make env handling more robust

[BradleyGoulding]

This is a potential fix for #75

It filters the --env-file process to ensure it only passes valid formatted env values

[g105b]

Hey thanks! I have an example repository at https://github.com/php-actions/example-phpunit that I will make a test for at some point soon. Feel free to create an example usage as a PR on that repo if you can do it before me.

[BradleyGoulding]

Sure, i will have a look, I need to create a negative test, so I will set an invalid env var, and with the current php-actions/composer@v6, and php-actions/phpunit@v4, this will fail. if i use my forks they will pass.

You can see the behaviour here: https://github.com/BradleyGoulding/example-phpunit/actions

Do you want me to just open the PR with the test that sets the environment up, pointing to current php-actions/composer@v6, and php-actions/phpunit@master, or wait till you merge the patch and update to include that?

My concern is that merging in an intentionally broken test pending the patch, will harm other work.