Editor: Add some missing terrain groupings (resolves #6643).

[ci skip]

(cherry picked from commit af72f75b2d)

changelog.md

@@ -25,6 +25,7 @@
      * Updated the modding instructions, helping add-on authors add extra factions etc.
  ### Editor
    * Add documentation for the magenta D and special terrain overlays (PR #6460).
+   * Added some missing terrain groupings (issue #6643)
  ### Multiplayer
    * Fixed updating add-ons when joining a game that requires a new version (issue #6383).
    * Add a `/clear` command for the lobby-chat window.

data/core/terrain.cfg

@@ -396,7 +396,7 @@ Most units receive 20 to 40% defense in sand."
     editor_name= _ "Snowbits"
     string=^Esa
     aliasof=_bas
-    editor_group=embellishments
+    editor_group=embellishments, frozen
 [/terrain_type]
 
 [terrain_type]
@@ -2143,7 +2143,7 @@ Merfolk and nagas have 60% defense in submerged villages, whereas land based uni
     aliasof=Ct
     unit_height_adjust=3
     recruit_onto=yes
-    editor_group=castle
+    editor_group=castle, frozen
 [/terrain_type]
 
 [terrain_type]