fix: add Splunk 9.2 to the matrix [DO NOT MERGE]

[mkolasinski-splunk]

[DO NOT MERGE] - latest 9.2 splunk docker image is not handling properly HEC token creation via env vars, which will cause failures in TAs CI.

Adding Splunk 9.2 to the matrix as it was recently released: https://docs.splunk.com/Documentation/Splunk/latest/ReleaseNotes/MeetSplunk