roll deps (KhronosGroup#6273)

* Roll external/abseil_cpp/ 5ad0bfb7a..747f9c9fd (3 commits)

abseil/abseil-cpp@5ad0bfb...747f9c9

Created with:
  roll-dep external/abseil_cpp

* Roll external/spirv-headers/ a8637796c..3397e1e4f (1 commit)

KhronosGroup/SPIRV-Headers@a863779...3397e1e

Created with:
  roll-dep external/spirv-headers

---------

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': '5ad0bfb7ab424355d95065ff7b5f5b920f3cac0d',
+  'abseil_revision': '747f9c9fd244016e1d3da41f51b17aa03b96d6d3',
 
   'effcee_revision': '514b52ec61609744d7e587d93a7ef9b60407ab45',
 
@@ -14,7 +14,7 @@ vars = {
 
   're2_revision': '6569a9a3df256f4c0c3813cb8ee2f8eef6e2c1fb',
 
-  'spirv_headers_revision': 'a8637796c28386c3cf3b4e8107020fbb52c46f3f',
+  'spirv_headers_revision': '3397e1e4fe0a9964e1837c2934b81835093494b8',
 
   'mimalloc_revision': '09a27098aa6e9286518bd9c74e6ffa7199c3f04e',
 }