The new regression test constructed `reqwest::Client::new()`, which
panics in the nix build sandbox: with no system CA store,
`ClientBuilder::build()` reaches `rustls_platform_verifier::Verifier::new()`
and fails, and `new()` is `build().expect(..)`. The test passed locally
because a devshell has `/etc/ssl/certs`, and failed in CI.
Disabling certificate verification takes the branch that installs a
no-op verifier and never consults the platform store, so the client
builds anywhere. That is sound in this test and nowhere else: nothing is
sent, the request is built and its bytes are inspected. The helper says
so at the point someone would otherwise object to it.
Found by reading reqwest's `ClientBuilder::build()` rather than trying
builder flags: the first repro attempt — pointing `SSL_CERT_FILE` and
`SSL_CERT_DIR` at nothing — did not reproduce, so any fix verified
against it would have been verified against nothing.
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