std.Io.Writer.print: support .enum_literal in 't' format specifier

[snoire]

The {t} format specifier in Writer.print prints the tag name for enums and errors. However, it did not support enum literals, which caused an invalidFmtError when an enum literal was passed to it.

This simple change adds .enum_literal to the type check, allowing enum literals to be printed using their tag name, which makes the behavior consistent with other enum types.

[squeek502]

Mind adding

    try expectFmt("hello_world", "{t}", .{.hello_world});

to

zig/lib/std/fmt.zig

Lines 1250 to 1252 in 416bf1d

	test "enum-literal" {
	try expectFmt(".hello_world", "{}", .{.hello_world});
	}

?

[snoire]

Thanks for the suggestion! I've added the test case.