Mark failing curl test on macOS x64 as xfail

Exactly these tests are failing on all our macOS x64 CI runners for
about a week.  For now we mark them as xfail, to get back to a green
CI pipeline.

Closes GH-16002.

ext/curl/tests/bug48203_multi.phpt

@@ -2,6 +2,12 @@
 Variation of bug #48203 with curl_multi_exec (Crash when file pointers passed to curl are closed before calling curl_multi_exec)
 --EXTENSIONS--
 curl
+--SKIPIF--
+<?php
+if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
+    die("xfail Test fails for unknown reasons");
+}
+?>
 --FILE--
 <?php
 include 'server.inc';

ext/curl/tests/bug71523.phpt

@@ -2,6 +2,12 @@
 Bug #71523 (Copied handle with new option CURLOPT_HTTPHEADER crashes while curl_multi_exec)
 --EXTENSIONS--
 curl
+--SKIPIF--
+<?php
+if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
+    die("xfail Test fails for unknown reasons");
+}
+?>
 --FILE--
 <?php
 

ext/curl/tests/curl_basic_018.phpt

@@ -4,6 +4,12 @@ Test curl_setopt() with curl_multi function with basic functionality
 TestFest 2009 - AFUP - Thomas Rabaix <[email protected]>
 --EXTENSIONS--
 curl
+--SKIPIF--
+<?php
+if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
+    die("xfail Test fails for unknown reasons");
+}
+?>
 --FILE--
 <?php
   include 'server.inc';

ext/curl/tests/curl_multi_getcontent_basic3.phpt

@@ -5,6 +5,12 @@ Rein Velt ([email protected])
 #TestFest Utrecht 20090509
 --EXTENSIONS--
 curl
+--SKIPIF--
+<?php
+if (getenv("GITHUB_ACTIONS") && PHP_OS_FAMILY === "Darwin" && php_uname("m") === "x86_64") {
+    die("xfail Test fails for unknown reasons");
+}
+?>
 --FILE--
 <?php
     //CURL_MULTI_GETCONTENT TEST