Update docker runner to resolve docker path using /usr/bin/env

[thelovekesh]

Sometimes, the WP CLI process doesn't have access to PATH and it gives an error. This PR aims to resolve those binary using env which is already done for binaries like mysql.

Related: #5935

[thelovekesh]

@swissspidy Should we change these occurrences with Utils\force_env_on_nix_systems()?

wp-cli/php/utils.php

Line 1782 in 46051ea

$result = Process::create( '/usr/bin/env which mysql', null, null )->run();

[swissspidy]

Probably? cc @schlessera for 2nd opinion