Skip WMS_GetPrint_SRS test in PyQgsServer

As per discussion with Alessandro Pasotti

cherry-picked from 2af1e9f

Author: dakcarto

tests/src/python/test_qgsserver.py

@@ -600,6 +600,7 @@ def test_wms_getprint_basic(self):
         r, h = self._result(self.server.handleRequest(qs))
         self._img_diff_error(r, h, "WMS_GetPrint_Basic")
 
+    @unittest.skip('Randomly failing to draw the map layer')
     def test_wms_getprint_srs(self):
         qs = "&".join(["%s=%s" % i for i in list({
             "MAP": urllib.quote(self.projectPath),