Bump up v1.7.3.pre.1 #32

Job	Run time
ruby-versions / Generate Ruby versions	4s
test (2.5, ubuntu-latest)	27s
test (2.5, macos-latest)	1m 20s
test (2.5, windows-latest)	1m 47s
test (2.6, ubuntu-latest)	36s
test (2.6, macos-latest)	1m 43s
test (2.6, windows-latest)	2m 43s
test (2.7, ubuntu-latest)	48s
test (2.7, macos-latest)	1m 0s
test (2.7, windows-latest)	2m 25s
test (3.0, ubuntu-latest)	26s
test (3.0, macos-latest)	35s
test (3.0, windows-latest)	1m 27s
test (3.1, ubuntu-latest)	18s
test (3.1, macos-latest)	44s
test (3.1, windows-latest)	2m 38s
test (3.2, ubuntu-latest)	21s
test (3.2, macos-latest)	45s
test (3.2, windows-latest)	2m 10s
test (head, ubuntu-latest)	25s
test (head, macos-latest)	40s
test (head, windows-latest)	2m 5s
test (jruby, ubuntu-latest)	5m 44s
test (jruby-head, ubuntu-latest)	6m 56s
test (truffleruby, ubuntu-latest)	2m 32s
test (truffleruby-head, ubuntu-latest)	3m 17s
	43m 56s

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