langref: incorrect use of the term "enum variant" in enums.zig

[perillo]

The doctest enums.zig in the #enum section has this example:

// An enum variant of different types can be switched upon.
const Foo = enum {
    string,
    number,
    none,
};
test "enum variant switch" {
    const p = Foo.number;
    const what_is_it = switch (p) {
        Foo.string => "this is a string",
        Foo.number => "this is a number",
        Foo.none => "this is a none",
    };
    try expect(mem.eql(u8, what_is_it, "this is a number"));
}

However, IMHO, the term enum invariant is used incorrectly; this term can be used in Rust, but not in Zig. Also, the enum fields all have the same type.

NOTE: the term enum invariant is also used in #12186.

[gettsu]

I am looking to address this issue.
I'm thinking to modify

1. "// An enum variant of different types can be switched upon." to "// Enums can be switched upon"
2. "test "enum variant switch"" to "tests "enum switch""

I'll submit a pull request if this is okay.