Document PHP 8.4.0 change to http_build_query() in relation to BackedEnums (#4988)

Explain that `http_build_query()` didn't convert BackedEnums to their scalar equilvalents, and instead converted them to objects.

Author: liamduckett

reference/url/functions/http-build-query.xml

@@ -109,6 +109,13 @@
      </row>
     </thead>
     <tbody>
+     <row>
+      <entry>8.4.0</entry>
+      <entry>
+       Prior to PHP 8.4.0, <interfacename>BackedEnum</interfacename> properties of
+       <parameter>data</parameter> were converted to objects, rather than their scalar equivalents.
+      </entry>
+     </row>
      <row>
       <entry>8.0.0</entry>
       <entry>