avoid false failure for long path

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With very long path, socket path may be truncated before $socketFilePrefix,

In which case, test is failing with Socket files were not found message

This is a false failure, as the log contains the expected message:

[01-Jul-2025 05:38:07] WARNING: [pool fpm_pool] cannot bind to UNIX socket '/builddir/build/BUILD/php85-php-8.5.0_DEV.20250630-build/php-src-c9249e2d3aa401bda5d9a3071e86e0594807ed00/sapi/fpm/tests/socket-file-fpm-unix-socket-too-long-filename-but-starts-anyway-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000.sock' as path is too long (found length: 244, maximal length: 108), trying cut socket path instead '/builddir/build/BUILD/php85-php-8.5.0_DEV.20250630-build/php-src-c9249e2d3aa401bda5d9a3071e86e0594807ed00/s'

So only report about Socket file is the same as configured (failed test because path not truncated)

Also avoid the Warning: Undefined array key 0 in .../sapi/fpm/tests/socket-uds-too-long-filename-start.php on line 41

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Ping @JoshuaBehrens who adds this test