Update to windows-sys 0.61

[hanna-kruppe]

Tokio and mio already updated to windows-sys 0.61, so socket2 requiring 0.60 makes it hard to avoid multiple copies of windows-sys. In addition, 0.61 finally drops the dependency on large pre-built import libraries (from windows-targets) in favor of Rust's raw-dylib feature.

Since no code changes are needed, I relaxed the version requirement (still allowing 0.60) to avoid increasing socket2's MSRV.

[hanna-kruppe]

FWIW, the MSRV bump would be 1.70 -> 1.71. It seems that CI doesn't exercise the windows + Rust 1.70 combination, but it would give this error:

error: package `windows-link v0.2.1` cannot be built because it requires rustc 1.71 or newer, while the currently active rustc version is 1.70.0
Either upgrade to rustc 1.71 or newer, or use
cargo update -p windows-link@0.2.1 --precise ver
where `ver` is the latest version of `windows-link` supporting rustc 1.70.0

which unfortunately makes the wrong suggestion, the fix is to run

cargo update windows-sys --precise 0.60.2