Tag off low-priority SyntaxError specs

These are not commonly-used syntax and not raising the correct
error here does not impact typical usage.

spec/tags/ruby/language/delegation_tags.txt

@@ -0,0 +1,3 @@
+fails(low-priority missing syntax error):delegation with def(*) within a block that accepts anonymous rest within a method that accepts anonymous rest does not allow delegating rest
+fails(low-priority missing syntax error):delegation with def(**) within a block that accepts anonymous kwargs within a method that accepts anonymous kwargs does not allow delegating kwargs
+fails(low-priority missing syntax error):delegation with def(&) within a block that accepts anonymous block within a method that accepts anonymous block does not allow delegating a block

spec/tags/ruby/language/hash_tags.txt

@@ -1,3 +1,4 @@
 fails:The ** operator makes a copy when calling a method taking a positional Hash
 fails:The ** operator hash with omitted value raises a SyntaxError when the hash key ends with `!`
 fails:The ** operator hash with omitted value raises a SyntaxError when the hash key ends with `?`
+fails(low-priority missing syntax error):Hash literal raises a SyntaxError at parse time when Symbol key with invalid bytes and 'key: value' syntax used

spec/tags/ruby/language/source_encoding_tags.txt

@@ -0,0 +1,2 @@
+fails(low-priority missing syntax error):Source files encoded in UTF-16 LE with a BOM are invalid because they contain an invalid UTF-8 sequence before the encoding comment
+fails(low-priority missing syntax error):Source files encoded in UTF-16 BE with a BOM are invalid because they contain an invalid UTF-8 sequence before the encoding comment