Update ICU (trusted)

Rolling v8/third_party/icu: https://chromium.googlesource.com/chromium/deps/icu/+log/bbdc7d8..20f8ac6

Make references to //third_party/icu relative (Filip Filmar)
https://chromium.googlesource.com/chromium/deps/icu/+/20f8ac6

R=v8-waterfall-sheriff@grotations.appspotmail.com,mtv-sf-v8-sheriff@grotations.appspotmail.com,ftang@chromium.org

Change-Id: I87063f9ec7b4ef8491c43ad8e1902e2741dd0e49
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3886397
Bot-Commit: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Commit-Queue: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#83093}

DEPS

@@ -223,7 +223,7 @@ deps = {
   'third_party/googletest/src':
     Var('chromium_url') + '/external/github.com/google/googletest.git' + '@' + 'af29db7ec28d6df1c7f0f745186884091e602e07',
   'third_party/icu':
-    Var('chromium_url') + '/chromium/deps/icu.git' + '@' + 'bbdc7d8936bd9b896ff9c9822b697554b73c1c9d',
+    Var('chromium_url') + '/chromium/deps/icu.git' + '@' + '20f8ac695af59b6c830def7d4e95bfeb13dd7be5',
   'third_party/instrumented_libraries':
     Var('chromium_url') + '/chromium/src/third_party/instrumented_libraries.git' + '@' + 'e09c4b66b6e87116eb190651421f1a6e2f3b9c52',
   'third_party/ittapi': {