Add test for Unicode 15.1

Doesn't actually change anything, apart from when MoarVM supports
Unicode 15.1, then no changes will be needed here anymore.

Test based on the fact that 15.1 added a

    CJK Unified Ideographs Extension I

block (range 2EBF0..2EE5F) as described on

    https://www.unicode.org/versions/Unicode15.1.0/

src/core.c/Unicode.rakumod

@@ -38,6 +38,7 @@ my class Unicode {
       '13.0' => 0x1F972.chr,
       '14.0' =>  0x061D.chr,
       '15.0' =>  0x0CF3.chr,
+      '15.1' => 0x2EE5F.chr,
     # PLEASE ADD NEWER UNICODE VERSIONS HERE, AS SOON AS THE UNICODE
     # CONSORTIUM HAS RELEASED A NEW VERSION
     ).first(*.value.uniprop('Age') ne 'Unassigned', :end).key.Version;