bug #958 Fix testMemoryLimit on PHP installed using Nix (shyim)

This PR was merged into the 1.x branch.

Discussion
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Fix testMemoryLimit on PHP installed using Nix

With PHP from Nix `php_ini_loaded_file()` returns false as the setup does not have a root `php.ini`

The test just assert was just wrong

```
1) Symfony\Flex\Tests\ScriptExecutorTest::testMemoryLimit
Expectation failed for method name is "execute" when invoked zero or more times
Parameter 0 for invocation Composer\Util\ProcessExecutor::execute(''/nix/store/x8czkm08bkf1979pf...nd.php', Closure Object (...), null): int does not match expected value.
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-''/nix/store/x8czkm08bkf1979pfv1f4d9h2zgh8k9n-php-with-extensions-8.1.12/bin/php' '--php-ini=' '-d memory_limit=32M' ./command.php'
+''/nix/store/x8czkm08bkf1979pfv1f4d9h2zgh8k9n-php-with-extensions-8.1.12/bin/php' '-d memory_limit=32M' ./command.php'

/Users/shyim/Code/flex-plugin/src/ScriptExecutor.php:58
/Users/shyim/Code/flex-plugin/tests/ScriptExecutorTest.php:56
```

Commits
-------

5b8dfa3 Fix testMemoryLimit on PHP installed using Nix

Author: nicolas-grekas