misc: Enforce using TLS1.2 or later for tz curl client

The tz database is not read using curl the way that the code is currently built.
However, if this were switched make sure to enforce using TLS1.2 or higher.

velox/external/date/tz.cpp

@@ -2848,6 +2848,8 @@ download_to_string(const std::string& url, std::string& str)
         return false;
     std::string version;
     curl_easy_setopt(curl.get(), CURLOPT_USERAGENT, "curl");
+    // Use TLS 1.2 or later.
+    curl_easy_setopt(curl.get(), CURLOPT_SSLVERSION, static_cast<long>(CURL_SSLVERSION_TLSv1_2));
     curl_easy_setopt(curl.get(), CURLOPT_URL, url.c_str());
     curl_write_callback write_cb = [](char* contents, std::size_t size, std::size_t nmemb,
                                       void* userp) -> std::size_t