Fix NamedTempFile constructors

[BenjaminBrienen]

OpenOptions::create_new documentation:

/// The file must be opened with write or append access in order to create
/// a new file.
///
/// ```no_run
/// use std::fs::OpenOptions;
///
/// let file = OpenOptions::new().write(true)
///                              .create_new(true)
///                              .open("foo.txt");
/// ```

First commit demonstrates failing test. Error is like: creating or truncating a file requires write or append access.

https://github.com/rust-lang/rust-analyzer/actions/runs/33827828269/job/100884169555?pr=23292

Second commit is the fix. Can squash if approved.

I think this wasn't caught because it is only used in crates/proc-macro-srv/src/dylib.rs and only in #[cfg(windows)] and I'm not sure whether this issue appears on Windows in this circumstance.

[BenjaminBrienen]

This is more complicated than it needs to be because I copy pasted these from what I was doing in another branch. I can simplify it if is a bother.

View changes since the review

[ChayimFriedman2]

I thought I already did that 🤔