chore: link anchor for "subobject fibration"

Author: TOTBWF

src/Cat/Displayed/Instances/Subobjects.lagda.md

@@ -32,7 +32,7 @@ open Displayed
 ```
 -->
 
-# The fibration of subobjects {defines="poset-of-subobjects subobject"}
+# The fibration of subobjects {defines="poset-of-subobjects subobject subobject-fibration"}
 
 Given a base category $\cB$, we can define the [[displayed category]] of
 _subobjects_ over $\cB$. This is, in essence, a restriction of the