[licenses] Updates ICU license regexp and URL

New file in the ICU library use the https scheme for the URL
instead of prior http to declare the license, leading to
the 'unmatched potential copyright' message.

This change removes the issue.

Author: filmil

tools/licenses/lib/licenses.dart

@@ -307,6 +307,7 @@ abstract class License implements Comparable<License> {
         body = system.File('data/mit').readAsStringSync();
         type = LicenseType.mit;
         break;
+      case 'https://www.unicode.org/copyright.html':
       case 'http://www.unicode.org/copyright.html':
         body = system.File('data/unicode').readAsStringSync();
         type = LicenseType.icu;

tools/licenses/lib/patterns.dart

@@ -1156,7 +1156,7 @@ final List<MultipleVersionedLicenseReferencePattern> csReferencesByUrl = <Multip
     pattern: RegExp(
       kIndent +
       r'(?:©|Copyright (©|\(C\))) 20.. and later: Unicode, Inc. and others.[ *]*\n'
-      r'^\1\2License & terms of use: (http://www.unicode.org/copyright.html)',
+      r'^\1\2License & terms of use: (https?://www.unicode.org/copyright.html)',
       multiLine: true,
       caseSensitive: false,
     )