Upgrade to Gradle 8.5

[msfroh]

This is in preparation for the upgrade to JDK 21.

Description

This is in preparation for the upgrade to JDK 21.

Issues Resolved

Related to https://github.com/opensearch-project/OpenSearch/issues/10334

Check List

• [ ] ~New functionality includes testing.~
  • [ ] ~All tests pass~
• [ ] ~New functionality has been documented.~
  • [ ] ~New functionality has javadoc added~
• [x] Commits are signed as per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (f7570dd) 83.30% compared to head (bc79a41) 83.30%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #213 +/- ## ========================================= Coverage 83.30% 83.30% Complexity 337 337 ========================================= Files 43 43 Lines 1270 1270 Branches 155 155 ========================================= Hits 1058 1058 Misses 134 134 Partials 78 78 ```

:umbrella: View full report in Codecov by Sentry.
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[reta]

@msfroh could you please add JDK-21 to build matrix (Github Actions)? thank you

[opensearch-trigger-bot[bot]]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-213-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 af87aa78a352ba7e4e61004165f361814243a4e3
# Push it to GitHub
git push --set-upstream origin backport/backport-213-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-213-to-2.x.