fix CompressionStrategyTest

[clintropolis]

Fixes an issue caused by a modification to CompressionStrategyTest in #12408 that was closing buffers allocated by the compression strategy instead of allowing the Closer to do it, leading to exceptions such as #12408 (comment) appearing when running the tests. After making these changes, I am unable to trigger the issue anymore.

[clintropolis]

have repeated the tests a few times, and haven't seen the original issue. I am seeing another occasional failure, this one seems a bit different and i've only seen on jdk15

[INFO] Running org.apache.druid.segment.data.CompressedVSizeColumnarIntsSupplierTest
#
[thread 11561 also had an error]
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007fa7b8035f67, pid=10264, tid=11562
#
# JRE version: OpenJDK Runtime Environment (15.0.2+7) (build 15.0.2+7-27)
# Java VM: OpenJDK 64-Bit Server VM (15.0.2+7-27, mixed mode, sharing, tiered, compressed oops, g1 gc, linux-amd64)
# Problematic frame:
# C  [libc.so.6+0x7ff67]
[timeout occurred during error reporting in step "printing problematic frame"] after 30 s.
# No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# An error report file with more information is saved as:
# /home/travis/build/apache/druid/processing/hs_err_pid10264.log
# [ timer expired, abort... ]
Aborted

It doesn't occur consistently, and I wouldn't guess it is actually related to the changes in this PR.