Ignore flaky shadertext2_pdf-poppler tests on Mac-10.7 Release builds

expectations/gm/Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Release/expected-results.json

Index: expectations/gm/Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Release/expected-results.json
===================================================================
--- expectations/gm/Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Release/expected-results.json	(revision 11523)
+++ expectations/gm/Test-Mac10.7-MacMini4.1-GeForce320M-x86_64-Release/expected-results.json	(working copy)
@@ -11016,8 +11016,9 @@
         ]
       ], 
       "bugs": [
-        1578
+        1578, 1692
       ], 
+      "ignore-failure": true, 
       "reviewed-by-human": false
     }, 
     "shadertext3_565.png": {
@@ -13119,4 +13120,4 @@
       "reviewed-by-human": false
     }
   }
-}
+}