Include the exit code and stderr when a bin/rector output assertion fails

[SanderMuller]

testConsoleOutput asserts on getOutput() alone, so when the spawned bin/rector writes nothing to stdout the failure is a diff against an empty string with no reason attached. The exit code and anything on stderr are both dropped.

That is exactly what a failing run looks like in PHPStan's integration job, where all three cases report '' including the --version one:

1) ...testConsoleOutput@Version with data ('/usr/bin/php8.4 bin/rector --version', 'Rector @package_version@\n')
-'Rector @package_version@
+''

Nothing there says whether the process failed to start, fataled, or exited non-zero.

assertSame() takes a message, so this puts both in the failure:

exit code 0, stderr:
Failed asserting that two strings are identical.

No new test: the change is in the assertion itself, and I checked it renders by pointing one expectation at a deliberately wrong string. tests/Bin stays green (3 tests, 3 assertions), vendor/bin/ecs is clean on the file, and vendor/bin/phpstan analyse tests/Bin/RectorTest.php reports no errors.

getExitCode() is nullable, so it is rendered with %s and a fallback rather than %d, which would print a misleading 0 for a process that never started.