chore(all): auto-regenerate .pb.go files (googleapis#525)

This is an auto-generated regeneration of the .pb.go files by
cloud.google.com/go/internal/gapicgen. Once this PR is submitted, genbot will
update the corresponding PR to depend on the newer version of go-genproto, and
assign reviewers. Whilst this or any regen PR is open in go-genproto, genbot
will not create any more regeneration PRs. If all regen PRs are closed,
gapicgen will create a new set of regeneration PRs once per night.

If you have been assigned to review this PR, please:

- Ensure that CI is passing. If it's failing, it requires your manual attention.
- Approve and submit this PR if you believe it's ready to ship. That will prompt
genbot to assign reviewers to the google-cloud-go PR.

Corresponding google-cloud-go PR: googleapis/google-cloud-go#3648

Changes:

feat(channel): Add Pub/Sub endpoints for Cloud Channel API.
  PiperOrigin-RevId: 355059873
  Source-Link: googleapis/googleapis@6ef9eae

chore: upgrade gapic-generator-python to 0.40.5
  PiperOrigin-RevId: 354996675
  Source-Link: googleapis/googleapis@20712b8

feat(osconfig/agentendpoint): add ApplyConfigTask to AgentEndpoint API
  PiperOrigin-RevId: 354960512
  Source-Link: googleapis/googleapis@e7c74bb