regex: don't hold state lock when pushing

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/533>

text/regex/src/gstregex/imp.rs

@@ -113,6 +113,8 @@ impl RegEx {
             );
         }
 
+        drop(state);
+
         self.srcpad.push(outbuf)
     }
 }