Changed accordingly to
rust-lang/rust#149400

```
error: this assertion has a constant value
 --> crates/build-rs-test-lib/src/lib.rs:3:5
  |
3 |     assert!(cfg!(did_run_build_script));
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = help: consider moving this into a const block: `const { assert!(..) }`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/rust-1.92.0/index.html#assertions_on_constants
  = note: `-D clippy::assertions-on-constants` implied by `-D warnings`
  = help: to override `-D warnings` add `#[allow(clippy::assertions_on_constants)]`
```

A bit annoying we can't have `lint.workspace = true` for this crate yet

### What does this PR try to resolve?

This PR backports #16385 along with some test fixes from #16380 to make
CI happy.

### How to test and review this PR?

r? @weihanglo

With version 0.4.84, cargo was failing on FreeBSD 13.5 and 14.3 every
time, with errors like this:

```
    Updating crates.io index
error: failed to get `futures` as a dependency of package `tokio-file v0.11.0 (/tmp/cirrus-ci-build)`
Caused by:
  download of config.json failed
Caused by:
  failed to download from `https://index.crates.io/config.json`
Caused by:
  [60] SSL peer certificate or SSH remote key was not OK (SSL certificate OpenSSL verify result: unable to get local issuer certificate (20))
```

Fixes #16357

Beta backports
- 389962f

In order to make CI pass, the following PRs are also cherry-picked:

- 

See also

* [#t-cargo > [beta-1.93] nominate backport curl
downgrade](https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/.5Bbeta-1.2E93.5D.20nominate.20backport.20curl.20downgrade/with/563873939)
*
#16357 (comment)