[PhpUnitBridge] Fix finding a config file given by its exact name

The .dist.xml support rewrite dropped the exact-name check, so an
explicitly given config file (-c custom.xml) was only probed with the
.xml/.xml.dist/.dist.xml suffixes appended and the wrapper silently
ignored the SYMFONY_PHPUNIT_* settings it contains (phpunit itself still
received it through passthrough). Probe the verbatim name after the
suffixed candidates: probing it first would make the default "phpunit"
lookup resolve to an extensionless phpunit binary or shim in the working
directory, shadowing phpunit.xml(.dist).

Author: YumeNikki101

bin/simple-phpunit.php

@@ -44,6 +44,12 @@
                 }
             }
 
+            // probe the verbatim name last so that the default "phpunit" lookup keeps
+            // resolving to phpunit.xml(.dist) when an extensionless "phpunit" file exists
+            if (file_exists($probableConfig)) {
+                return $probableConfig;
+            }
+
             return null;
         };