Adapt spec tests to not use UTF-32BE or UTF-16BE strings with trailin… #5028

Job	Run time
build native	13m 12s
build jvm	6m 27s
ruby/spec on CRuby 3.0	3m 26s
lint	14m 35s
ruby/spec on CRuby 3.1	3m 27s
ruby/spec on CRuby 3.2	3m 13s
fast specs	1m 48s
specs :truffle	14m 33s
test integration	9m 29s
specs :language :core	12m 33s
specs :library :cext :security :command_line :tracepoint	9m 14s
test native	3m 3s
run MRI tests on native	19m 22s
	1h 54m 22s

Provide feedback