Skip SkSharedMutexMultiThreaded test on TSAN bot while investigating.

The ~ means "don't run this".  This keeps all the other bots running the code, skipping it only on the whiny TSAN bot.

BUG=skia:3997

Review URL: https://codereview.chromium.org/1213033003

tools/dm_flags.json

@@ -946,7 +946,8 @@
     "decode", 
     "Hopstarter-Mac-Folders-Apple.ico", 
     "--match", 
-    "~Math"
+    "~Math", 
+    "~SkSharedMutexMultiThreaded"
   ], 
   "Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-Valgrind": [
     "--matrix", 

tools/dm_flags.py

@@ -148,8 +148,9 @@ def get_args(bot):
   match = []
   if 'Valgrind' in bot: # skia:3021
     match.append('~Threaded')
-  if 'TSAN' in bot: # skia:3562
-    match.append('~Math')
+  if 'TSAN' in bot:
+    match.append('~Math')                        # skia:3562
+    match.append('~SkSharedMutexMultiThreaded')  # skia:3997
 
   if 'GalaxyS3' in bot:  # skia:1699
     match.append('~WritePixels')