deps: bump minimum ICU version to 71

Refs: v8/v8@3ae4277
PR-URL: #44741
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

tools/icu/icu_versions.json

@@ -1,3 +1,3 @@
 {
-    "minimum_icu": 69
+    "minimum_icu": 71
 }