[Release] Fix verify-release-candidate.sh since pip3 seems to no longer be in miniconda

[asfimport]

Reporter: Krisztian Szucs / @kszucs
Assignee: Wes McKinney / @wesm

Related issues:

• [Release] Archery does not use correct integration test args (is duplicated by)

PRs and other links:

• GitHub Pull Request #6348

_{Note: This issue was originally created as ARROW-7760. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 6348
#6348