[2.0.x] Async Http Client 2.15.0 + netty-reactive-streams upgrade (backport #1299) by @mkurz

[mergify]

• CVE-2026-45300 GHSA-fmxf-pm6p-7xgm
• https://github.com/AsyncHttpClient/async-http-client/releases/tag/async-http-client-project-2.15.0

Change should be totally ok:
AsyncHttpClient/async-http-client@async-http-client-project-2.14.5...async-http-client-project-2.15.0#diff-87ac35b16332182a11ef31022ced078c748ec8d34ce26ee622bc046c359da55f

AHC 2.15.0 also upgrades to latest netty 4.1.133

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This is an automatic backport of pull request #1299 done by Mergify.

[mergify]

Cherry-pick of 794de39 has failed:

On branch mergify/bp/2.0.x/pr-1299
Your branch is up to date with 'origin/2.0.x'.

You are currently cherry-picking commit 794de39.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   project/Dependencies.scala

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally