add test for version of raku

Avoid issues where an older version might fail an example/signature test.

Author: coke

xt/01-raku-version.t

@@ -0,0 +1,19 @@
+#!/usr/bin/env raku
+
+use lib $*PROGRAM.parent(2).child('lib');
+use Test;
+
+=begin overview
+
+Verify that the version of rakudo used to run the tests is recent enough.
+
+To avoid issues with a mismatch on source or compilation testing.
+
+=end overview
+
+my $min = v2021.10;
+
+my $actual = $*RAKU.compiler.version;
+
+ok $actual >= $min, "using at least version $min for testing";
+