Install postgresql extensions under $out/share/postgresql

This fixes extensions after #62271 moved files from `$out/share` to
`$out/share/postgresql`.

pkgs/servers/sql/postgresql/ext/pg_similarity.nix

@@ -15,7 +15,7 @@ stdenv.mkDerivation {
   installPhase = ''
     mkdir -p $out/bin   # for buildEnv to setup proper symlinks
     install -D pg_similarity.so -t $out/lib/
-    install -D ./{pg_similarity--unpackaged--1.0.sql,pg_similarity--1.0.sql,pg_similarity.control} -t $out/share/extension
+    install -D ./{pg_similarity--unpackaged--1.0.sql,pg_similarity--1.0.sql,pg_similarity.control} -t $out/share/postgresql/extension
   '';
 
   meta = {