incremental: add test for ZON file without result type

test/incremental/change_zon_file_no_result_type

@@ -0,0 +1,24 @@
+#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+//#target=wasm32-wasi-selfhosted
+#update=initial version
+#file=main.zig
+const std = @import("std");
+pub fn main() !void {
+    try std.io.getStdOut().writeAll(@import("foo.zon").message);
+}
+#file=foo.zon
+.{
+    .message = "Hello, World!\n",
+    .a_number = 0,
+}
+#expect_stdout="Hello, World!\n"
+
+#update=change ZON file
+#file=foo.zon
+.{
+    .message = "Hello again, World!\n",
+    .b_number = 0,
+}
+#expect_stdout="Hello again, World!\n"