glx: Clarify a debug message

In GLX a "tag" usually means a context tag, "fbconfig attribute" is a
bit more obvious.

Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13002>

src/glx/glxext.c

@@ -617,7 +617,7 @@ __glXInitializeVisualConfigFromTags(struct glx_config * config, int count,
          break;
       default: {
             long int tagvalue = *bp++;
-            DebugMessageF("WARNING: unknown GLX tag from server: "
+            DebugMessageF("WARNING: unknown fbconfig attribute from server: "
                           "tag 0x%lx value 0x%lx\n", tag, tagvalue);
             break;
          }