Roll external/abseil_cpp/ 840da4a0f..56945519b (3 commits) (KhronosGroup#6235)

abseil/abseil-cpp@840da4a...5694551

Created with:
  roll-dep external/abseil_cpp

Co-authored-by: GitHub Actions[bot] <>

Author: github-actions[bot]

DEPS

@@ -3,7 +3,7 @@ use_relative_paths = True
 vars = {
   'github': 'https://github.com',
 
-  'abseil_revision': '840da4a0f04fc35ee84f70471f80cb1081af7e2a',
+  'abseil_revision': '56945519b5d17dcec0982ac6cdf4b6420f03c9c3',
 
   'effcee_revision': '8ce15c424e61a94ee27b5be0ec0ed036b158e6e3',