Fix false positive goleak test

[yurishkuro]

Which problem is this PR solving?

• The testutils package itself was being flagged as missing goleak check. The check was there, but without the package name, and the lint script was flagging it as false positive.
• Similar issue in pkg/cassandra/gocql/testutils
• Part of Enable and enforce goroutine leak checks in tests #5006

Description of the changes

1. Change package name of the test file so that the functions can be called with the usual package package name testutils.
2. change competing testutils import labels to satisfy the linter

How was this change tested?

• make goleak no longer shows this package

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 41.00%. Comparing base (34f6a25) to head (ae0ac0f).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #5315       +/-   ##
===========================================
- Coverage   95.15%   41.00%   -54.16%     
===========================================
  Files         340      212      -128     
  Lines       16666    10985     -5681     
===========================================
- Hits        15858     4504    -11354     
- Misses        617     6077     +5460     
- Partials      191      404      +213     

Flag	Coverage Δ
badger	12.25% <ø> (ø)
cassandra-3.x	21.14% <ø> (ø)
cassandra-4.x	21.14% <ø> (ø)
elasticsearch-5.x	17.70% <ø> (ø)
elasticsearch-6.x	17.70% <ø> (+0.01%)	⬆️
elasticsearch-7.x	17.75% <ø> (-0.02%)	⬇️
elasticsearch-8.x	17.82% <ø> (-0.02%)	⬇️
grpc	11.60% <ø> (+0.08%)	⬆️
kafka	11.84% <ø> (ø)
opensearch-1.x	17.76% <ø> (+0.01%)	⬆️
opensearch-2.x	17.75% <ø> (-0.02%)	⬇️
unittests	?

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