docs: fix inaccurate description of command targets

It isn't possible to have one target depend on a run_target, because
those produce no outputs and are always out of date. But the docs didn't
specify which types of target are valid here.

Correct the docs to align with the implementation.

Fixes #10198

docs/yaml/functions/custom_target.yaml

@@ -135,7 +135,7 @@ kwargs:
       argument. Useful for adding regen dependencies.
 
   depends:
-    type: list[tgt]
+    type: list[build_tgt | custom_tgt]
     description: |
       Specifies that this target depends on the specified
       target(s), even though it does not take any of them as a command

docs/yaml/functions/run_target.yaml

@@ -40,7 +40,7 @@ kwargs:
       the first item will find that command in `PATH` and run it.
 
   depends:
-    type: list[tgt]
+    type: list[build_tgt | custom_tgt]
     description: |
       A list of targets that this target depends on but which
       are not listed in the command array (because, for example, the