librustls: use '=' prefix specifier for rustls dep

and, in the `rustls_version_match()` test, ignore that prefix when
comparing the version.

Author: cpu

librustls/Cargo.toml

@@ -30,7 +30,7 @@ prefer-post-quantum = ["aws-lc-rs", "rustls/prefer-post-quantum"]
 
 [dependencies]
 # Keep in sync with RUSTLS_CRATE_VERSION in build.rs
-rustls = { version = "0.23.31", default-features = false, features = ["std", "tls12"] }
+rustls = { version = "=0.23.31", default-features = false, features = ["std", "tls12"] }
 webpki  = { workspace = true }
 libc = { workspace = true }
 log = { workspace = true }

librustls/tests/rustls_version.rs

@@ -51,7 +51,8 @@ fn rustls_version_match() {
         // Handle the `rustls = "x.y.z"` case
         None => rustls_dep.as_str(),
     }
-    .expect("missing rustls dependency version");
+    .expect("missing rustls dependency version")
+    .trim_start_matches("=");
 
     // Assert that rustls_version() returns a string of the form:
     //   $CRATE_NAME/$CRATE_VERSION/rustls/$RUSTLS_VERSION