fmt: Use left brace position instead of the right one

Fix a typo and add a test case.

lib/std/zig/parser_test.zig

@@ -7,6 +7,15 @@ test "zig fmt: trailing comma in container declaration" {
         \\const X = struct { foo: i32 align(4) = 1, bar: i32 align(4) = 2 };
         \\
     );
+    try testTransform(
+        \\const X = struct {
+        \\    foo: i32, bar: i8 };
+    ,
+        \\const X = struct {
+        \\    foo: i32, bar: i8
+        \\};
+        \\
+    );
 }
 
 test "zig fmt: trailing comma in fn parameter list" {

lib/std/zig/render.zig

@@ -1181,8 +1181,8 @@ fn renderExpression(
 
             // Check if the first declaration and the { are on the same line
             const src_has_newline = !tree.tokensOnSameLine(
+                container_decl.lbrace_token,
                 container_decl.fields_and_decls.at(0).*.firstToken(),
-                container_decl.rbrace_token,
             );
 
             // We can only print all the elements in-line if all the