[Backport 2.x] Change the testuser's password in some integration test cases into a stronger password

[opensearch-trigger-bot]

Backport e628c81 from #1428

[codecov]

Codecov Report

Merging #1432 (d9ccd63) into 2.x (8579406) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              2.x    #1432   +/-   ##
=======================================
  Coverage   71.67%   71.67%           
=======================================
  Files          88       88           
  Lines        2037     2037           
  Branches      272      277    +5     
=======================================
  Hits         1460     1460           
  Misses        511      511           
  Partials       66       66           

[RyanL1997]

CI is failing due to the version mismatch on 2.x branch. Will generate a version bump PR soon.
Error msg:

  ● start OpenSearch Dashboards server › create/get/update/list/delete internal user

    Failed to initialize plugins:
    	Plugin "securityDashboards" is only compatible with OpenSearch Dashboards version "2.7.0", but used OpenSearch Dashboards version is "2.7.1". (incompatible-version, /home/runner/work/security-dashboards-plugin/security-dashboards-plugin/OpenSearch-Dashboards/plugins/security-dashboards-plugin/opensearch_dashboards.json)

[RyanL1997]

Actually there is a version bump PR against 2.x branch: #1413. But this PR is bumping to 2.8.0, and I think the core dashboard's 2.x is in 2.7.1 based on the above error msg.. :/

[RyanL1997]

Closing this one due to the merge of #1437