Mark mixed_xfermodes_gpu on Win7 perspective bot as ignore-failure

expectations/gm/Test-Win7-ShuttleA-HD2000-x86-Release/expected-results.json

 {
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           9785004568147979273
         ]
       ], 
       "bugs": [
@@ skipping 9067 matching lines @@
       "reviewed-by-human": false
     }, 
     "mixed_xfermodes_gpu.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           16048358665979618885
         ]
       ], 
       "bugs": [
-        2146
+        2262
       ], 
-      "reviewed-by-human": false
+      "ignore-failure": true, 
+      "reviewed-by-human": true
     }, 
     "modecolorfilters_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           3160110095209559869
         ]
       ], 
       "bugs": [
         2146
@@ skipping 3993 matching lines @@
           15843716056234692659
         ]
       ], 
       "bugs": [
         2146
       ], 
       "reviewed-by-human": false
     }
   }
 }