[DependencyInjection] Update an error message

[javiereguiluz]

Q	A
Branch?	7.1
Bug fix?	no
New feature?	yes
Deprecations?	no
Issues	-
License	MIT

In a Symfony app I had the following:

#[Autowire('%env(kernel.project_dir)%')] private string $projectDir,

This should be instead:

#[Autowire('%kernel.project_dir%')] private string $projectDir,

In the console I saw this error message:

In my opinion, the error is not perfectly clear. That's why in this PR I propose some changes for your consideration. Thanks!

[fabpot]

Thank you @javiereguiluz.