Fallback missing constants with RFC3986_PARSER #297

Job	Run time
ruby-versions / Generate Ruby versions	1s
build (2.5 / ubuntu-latest)	18s
build (2.6 / ubuntu-latest)	20s
build (2.6 / macos-latest)	23s
build (2.7 / ubuntu-latest)	19s
build (2.7 / macos-latest)	30s
build (3.0 / ubuntu-latest)	5s
build (3.0 / macos-latest)	8s
build (3.1 / ubuntu-latest)	7s
build (3.1 / macos-latest)	11s
build (3.2 / ubuntu-latest)	10s
build (3.2 / macos-latest)	8s
build (3.3 / ubuntu-latest)	6s
build (3.3 / macos-latest)	9s
build (head / ubuntu-latest)	8s
build (head / macos-latest)	10s
build (jruby / ubuntu-latest)	25s
build (jruby / macos-latest)	26s
build (jruby-head / ubuntu-latest)	23s
build (jruby-head / macos-latest)	16s
build (truffleruby / ubuntu-latest)	16s
build (truffleruby / macos-latest)	13s
build (truffleruby-head / ubuntu-latest)	18s
build (truffleruby-head / macos-latest)	16s
	5m 46s

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