rust: bssl-crypto: fix clippy errors

> error: used `unwrap()` on an `Option` value

Bug: 500340788
Test: cargo clippy && cargo deny check && cargo test

Change-Id: I48354097916e9603a9293bf6541978ddfff1ca2b
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/92887
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

rust/bssl-crypto/src/ecdsa.rs

diff --git a/rust/bssl-crypto/src/ecdsa.rs b/rust/bssl-crypto/src/ecdsa.rs
index 922abc1..cdb61d1 100644
--- a/rust/bssl-crypto/src/ecdsa.rs
+++ b/rust/bssl-crypto/src/ecdsa.rs
@@ -242,7 +242,7 @@
     // Caller must make sure that the group of the key matches `C`,
     // or else it panics.
     pub(crate) fn from_ec_key(key: ec::Key) -> Self {
-        assert_eq!(key.get_group().unwrap(), C::group());
+        assert_eq!(key.get_group(), Some(C::group()));
         Self {
             key,
             marker: PhantomData,