[7.17](backport #40036) mod: update github.com/hashicorp/go-retryablehttp to v0.7.7

[mergify]

GHSA-v6v8-xj6m-xwqh

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• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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---

This is an automatic backport of pull request #40036 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of e1641ce has failed:

On branch mergify/bp/7.17/pr-40036
Your branch is up to date with 'origin/7.17'.

You are currently cherry-picking commit e1641ce577.
  (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)

Changes to be committed:
	modified:   CHANGELOG.next.asciidoc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   NOTICE.txt
	both modified:   go.mod
	both modified:   go.sum

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

[botelastic]

This pull request doesn't have a Team:<team> label.

[efd6]

check-docs check failing with

>> check: Checking source code for common problems
Error: some files are not up-to-date. Run 'mage fmt update' then review and commit the changes. Modified: [x-pack/elastic-agent/pkg/agent/control/cproto/control.pb.go x-pack/elastic-agent/pkg/agent/control/cproto/control_grpc.pb.go]

This is generated code and so should be ignored.