[Ruby 3.4] Add specs for SyntaxError raised when index assignment with block argument #2042

Job	Run time
RuboCop	48s
specs (ubuntu, 3.3.8)	1m 38s
specs (ubuntu, 3.4.4)	1m 35s
specs (macos, 3.4.4)	1m 12s
specs (macos, 3.3.8)	1m 8s
specs (macos, 3.2.8)	1m 32s
specs (windows, 3.4.4)	2m 54s
specs (ubuntu, 3.2.8)	1m 32s
specs (ubuntu, 3.4.4, --enable-frozen-string-literal)	1m 40s
specs (ubuntu, 3.4.4, --parser=parse.y)	1m 12s
specs (windows, 3.2.8)	3m 10s
specs (windows, 3.3.8)	2m 56s
	21m 17s

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