Reserve extension 678 (#2693)

For #2692.

Author: mahkoh

xml/vk.xml

@@ -30347,6 +30347,12 @@ endif::VK_KHR_internally_synchronized_queues[]
                 <enum value="&quot;VK_SEC_extension_675&quot;"             name="VK_SEC_EXTENSION_675_EXTENSION_NAME"/>
             </require>
         </extension>
+        <extension name="VK_EXT_extension_678" number="678" author="EXT" contact="Julian Orth @mahkoh" supported="disabled">
+            <require>
+                <enum value="0"                                            name="VK_EXT_EXTENSION_678_SPEC_VERSION"/>
+                <enum value="&quot;VK_EXT_extension_678&quot;"             name="VK_EXT_EXTENSION_678_EXTENSION_NAME"/>
+            </require>
+        </extension>
     </extensions>
     <formats>
         <format name="VK_FORMAT_R4G4_UNORM_PACK8" class="8-bit" blockSize="1" texelsPerBlock="1" packed="8">