Fix a -Wignored-qualifiers warning in trust_token_test.cc

The const bool doesn't do anything. While I'm here, make the methods
const.

Change-Id: Id8c31d5fcda6d8bc244c64b02b1d758e4eff6849
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/57185
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: Steven Valdez <svaldez@google.com>
Reviewed-by: Steven Valdez <svaldez@google.com>

crypto/trust_token/trust_token_test.cc

diff --git a/crypto/trust_token/trust_token_test.cc b/crypto/trust_token/trust_token_test.cc
index 6f952fb..ae4eb5c 100644
--- a/crypto/trust_token/trust_token_test.cc
+++ b/crypto/trust_token/trust_token_test.cc
@@ -313,9 +313,9 @@
     return static_cast<uint32_t>(7 + i);
   }
 
-  const TRUST_TOKEN_METHOD *method() { return method_; }
+  const TRUST_TOKEN_METHOD *method() const { return method_; }
 
-  const bool use_message() { return use_msg_; }
+  bool use_message() const { return use_msg_; }
 
  protected:
   void SetupContexts() {