Fix reuse of MatchData assigned to $~

    $~ = m = /a/.match("a").dup
    /b/ =~ "b"
    p m

[Bug #22381]

(cherry picked from commit ea3cd7e)

Author: jhawthorn

re.c

@@ -4622,6 +4622,7 @@ match_setter(VALUE val, ID _x, VALUE *_y)
 {
     if (!NIL_P(val)) {
         Check_Type(val, T_MATCH);
+        rb_match_busy(val);
     }
     rb_backref_set(val);
 }

test/ruby/test_regexp.rb

@@ -1025,6 +1025,19 @@ def test_match_setter
     assert_equal("foo", $&)
   end
 
+  def test_match_setter_with_copy
+    [:dup, :clone].each do |copy|
+      [false, true].each do |freeze|
+        m = /a/.match("a").public_send(copy)
+        m.freeze if freeze
+        $~ = m
+        /b/ =~ "b"
+        assert_equal("a", m[0], "#{copy}, freeze: #{freeze}")
+        assert_equal("b", $&)
+      end
+    end
+  end
+
   def test_match_without_regexp
     # create a MatchData for each assertion because the internal state may change
     test = proc {|&blk| "abc".sub("a", ""); blk.call($~) }