Fix test bug in WebContainer Servlet 31 FAT CDIUpgradeHandlerTest

[pmd1nh]

• I have considered the risk of behavior change or other zero migration impact (https://github.com/OpenLiberty/open-liberty/wiki/Behavior-Changes).
• If this PR fixes an Issue, the description includes "Fixes #FILLMEIN" or "Resolves #FILLMEIN" (verify release bug label if applicable: https://github.com/OpenLiberty/open-liberty/wiki/Open-Liberty-Conventions).
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fix build break 304040
Test Failure: com.ibm.ws.webcontainer.servlet31.fat.tests.CDIUpgradeHandlerTest.testCDIUpgradeHandlerUpgrade

[pmd1nh]

#build
(view Open Liberty Personal Build - ✅ completed successfully!)
#spawn.fullfat.buckets=com.ibm.ws.webcontainer.servlet.3.1_fat,com.ibm.ws.webcontainer.servlet.3.1_fat.2

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[LibbyBot]

Code analysis and actions

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• 3 FAT files were changed, added, or removed.

• Check that the build did not break the affected FAT suite(s).

• Please describe in a separate comment how you tested your changes.

[pmd1nh]

There is a stale class variable readListener object (as well as writeListener) that may cause this intermittent issue (can't recreate locally)

from the screenshot, the readListener.onDataAvailable (thread 0000002a) should NOT possibly read data when the readListener object is still initializing (in thread 0000002c). The fact there was actually a read onDataAvailable suggests that there was stale readListener object.