[test] Increase timeout for ssl_transport_security_test (#33789)

This test appears to be timing out more often lately. 

Example:
https://fusion2.corp.google.com/ci/kokoro/prod:grpc%2Fcore%2Fpull_request%2Flinux%2Fbazel_rbe%2Fgrpc_bazel_rbe_ubsan/activity/980ac4a8-da71-4b9b-838e-e9ea235820a1/log

test/core/tsi/BUILD

@@ -76,6 +76,7 @@ grpc_cc_test(
 
 grpc_cc_test(
     name = "ssl_transport_security_test",
+    timeout = "long",
     srcs = ["ssl_transport_security_test.cc"],
     data = [
         "//src/core/tsi/test_creds:badclient.key",