zig fmt: fix extra whitespace in StructInit with multiline strings

68d2f68 introduced special handling for StructInit fields
containing multiline strings to prevent inserting whitespace after =.
However, this logic didn't handle cases without a trailing comma,
which resulted in unwanted trailing whitespace.

Author: skewb1k

lib/std/zig/Ast/Render.zig

@@ -2056,7 +2056,8 @@ fn renderStructInit(
             const init_token = tree.firstToken(field_init);
             try renderToken(r, init_token - 3, .none); // .
             try renderIdentifier(r, init_token - 2, .space, .eagerly_unquote); // name
-            try renderToken(r, init_token - 1, .space); // =
+            const space_after_equal: Space = if (tree.nodeTag(field_init) == .multiline_string_literal) .none else .space;
+            try renderToken(r, init_token - 1, space_after_equal); // =
             try renderExpressionFixup(r, field_init, .comma_space);
         }
     }

lib/std/zig/parser_test.zig

@@ -5719,6 +5719,16 @@ test "zig fmt: no space before newline before multiline string" {
         \\        ,
         \\    };
         \\    _ = s2;
+        \\    const s3 = .{ .text =
+        \\        \\hello
+        \\        \\world
+        \\    , .comment = "test" };
+        \\    _ = s3;
+        \\    const s4 = .{ .comment = "test", .text =
+        \\        \\hello
+        \\        \\world
+        \\    };
+        \\    _ = s4;
         \\}
         \\
     );