fix(curl): Set PROXY_CAINFO curlopt with CAINFO, fixes HTTPS proxies

See discussion from: #6 (comment)

Co-Authored-By: coletdjnz <coletdjnz@proton.me>

curl_cffi/curl.py

@@ -272,6 +272,8 @@ def _ensure_cacert(self) -> None:
         if not self._is_cert_set:
             ret = self.setopt(CurlOpt.CAINFO, self._cacert)
             self._check_error(ret, "set cacert")
+            ret = self.setopt(CurlOpt.PROXY_CAINFO, self._cacert)
+            self._check_error(ret, "set proxy cacert")
 
     def perform(self, clear_headers: bool = True) -> None:
         """Wrapper for ``curl_easy_perform``, performs a curl request.