ARROW-13523: [C++] Normalize test executable name
ARROW-13523: [C++] Normalize test executable name

Use hyphens, not underscores

Closes #10818 from darionyaphet/reader_test

Authored-by: darion.yaphet <4970925dd050bad8b1e72e955f5ce1d13e05a20f@gmail.com>
Signed-off-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>

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