[Developer] Use ARROW_TMPDIR environment variable in the verification scripts instead of TMPDIR

[asfimport]

See discussion #6344 (comment)

Reporter: Krisztian Szucs / @kszucs
Assignee: Krisztian Szucs / @kszucs

PRs and other links:

• GitHub Pull Request #6718

_{Note: This issue was originally created as ARROW-7771. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 6718
#6718