checker: fix map init with enum keys (#12637)

vlib/v/checker/checker.v

@@ -7744,6 +7744,7 @@ pub fn (mut c Checker) map_init(mut node ast.MapInit) ast.Type {
 				continue
 			}
 			val := node.vals[i]
+			c.expected_type = key0_type
 			key_type := c.expr(key)
 			c.expected_type = val0_type
 			val_type := c.expr(val)

vlib/v/tests/map_init_with_enum_keys_test.v

@@ -0,0 +1,20 @@
+enum En {
+	ea
+	eb
+}
+
+struct St {
+mut:
+	m map[En]string
+}
+
+fn test_map_init_with_enum_keys() {
+	mut st := St{}
+
+	st.m = {
+		.ea: 'a'
+	}
+
+	println(st.m)
+	assert '$st.m' == "{ea: 'a'}"
+}