Blacklist check_small_sigma_offset on Chromecast

Bug: skia:6687
Change-Id: I4244b6345da5edd1ac6fe2225ed8c109a6e66a66
Reviewed-on: https://skia-review.googlesource.com/121347
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Eric Boren <borenet@google.com>

infra/bots/recipes/test.expected/Test-Chromecast-GCC-Chorizo-GPU-Cortex_A7-arm-Release-All.json

@@ -595,6 +595,7 @@
       "~animated-image-blurs",
       "~blur_0.01",
       "~blur_image_filter",
+      "~check_small_sigma_offset",
       "~imageblur2",
       "~lighting",
       "~longpathdash",

infra/bots/recipes/test.py

@@ -567,6 +567,7 @@ def dm_flags(api, bot):
       match.append('~animated-image-blurs')
       match.append('~blur_0.01')
       match.append('~blur_image_filter')
+      match.append('~check_small_sigma_offset')
       match.append('~imageblur2')
       match.append('~lighting')
       match.append('~longpathdash')