tests: ignore version test for cargo-c ctest

When running under `cargo ctest` the `rustls-ffi` import doesn't work
for this small integration test.

It's not worth debugging atm. Let's just ignore it for now and only run
the test from the normal 'cargo test' invocation where it works.

tests/rustls_version.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "capi"))]
 use std::fs::File;
 use std::io::Read;
 use std::path::PathBuf;