Roll ICU from f27805b7d7d8 to a86a32e67b8d (1 revision) (flutter#178859)

https://chromium.googlesource.com/chromium/deps/icu.git/+log/f27805b7d7d8..a86a32e67b8d

2025-11-03 ftang@chromium.org Fix undefined behavior front() call Cherry
pick undefined behavior fix from ICU PR3752

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/icu-sdk-flutter
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to ensure that a human
is aware of the problem.

To file a bug in ICU: https://github.com/unicode-org/icu
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Author: engine-flutter-autoroll

DEPS

@@ -260,7 +260,7 @@ deps = {
    Var('chromium_git') + '/external/github.com/google/flatbuffers' + '@' + '067bfdbde9b10c1beb5d6b02d67ae9db8b96f736',
 
   'engine/src/flutter/third_party/icu':
-   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + 'f27805b7d7d8618fa73ce89e9d28e0a8b2216fec',
+   Var('chromium_git') + '/chromium/deps/icu.git' + '@' + 'a86a32e67b8d1384b33f8fa48c83a6079b86f8cd',
 
    'engine/src/flutter/third_party/gtest-parallel':
    Var('chromium_git') + '/external/github.com/google/gtest-parallel' + '@' + '38191e2733d7cbaeaef6a3f1a942ddeb38a2ad14',