v.checker: turn `interface field ... must be initialized` to a notice temporarily

vlib/v/checker/checker.v

@@ -1175,8 +1175,8 @@ pub fn (mut c Checker) struct_init(mut node ast.StructInit) ast.Type {
 				// Do not allow empty uninitialized interfaces
 				sym := c.table.get_type_symbol(field.typ)
 				if sym.kind == .interface_ {
-					// TODO error
+					// TODO: should be an error instead, but first `ui` needs updating.
-					c.warn('interface field `${type_sym.name}.$field.name` must be initialized',
+					c.note('interface field `${type_sym.name}.$field.name` must be initialized',
 						node.pos)
 				}
 				// Do not allow empty uninitialized sum types

vlib/v/checker/tests/import_symbol_private_err.out

@@ -1,3 +1,15 @@
+vlib/v/checker/tests/import_symbol_private_err.vv:11:6: notice: interface field `io.ReaderWriterImpl.r` must be initialized
+    9 |     since(now())
+   10 |     _ = {'h': 2}.exists('h')
+   11 |     _ = ReaderWriterImpl{}
+      |         ~~~~~~~~~~~~~~~~~~
+   12 | }
+vlib/v/checker/tests/import_symbol_private_err.vv:11:6: notice: interface field `io.ReaderWriterImpl.w` must be initialized
+    9 |     since(now())
+   10 |     _ = {'h': 2}.exists('h')
+   11 |     _ = ReaderWriterImpl{}
+      |         ~~~~~~~~~~~~~~~~~~
+   12 | }
 vlib/v/checker/tests/import_symbol_private_err.vv:3:20: error: module `time` function `since()` is private
     1 | import v.scanner
     2 | import v.parser

vlib/v/checker/tests/interface_init_err.out

@@ -1,4 +1,4 @@
-vlib/v/checker/tests/interface_init_err.vv:15:7: error: interface field `Server.handler` must be initialized
+vlib/v/checker/tests/interface_init_err.vv:15:7: notice: interface field `Server.handler` must be initialized
    13 | 
    14 | fn main() {
    15 |     _ := Server{}