Don't invalidate container cache on user-interactions in the shell

[staabm]

refs phpstan/phpstan#14072 (comment)

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ENV variables used for building the container key sometimes change, based on user interactions in the shell.

it happens after you cd between folders and run PHPStan again.

see https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html

OLDPWD
The previous working directory as set by the cd builtin.

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I see another case: the container invalidates as soon as you re-size the shell window, because a ENV var exists which defines the LINES and COLUMNS in the window

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while I think this is just a workaround for a more general problem - I see no way atm to find out which ENV vars are relevant for us and which are not

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

Thank you!