Bump spiffe/spire-server from 1.15.0 to 1.15.1 in /docker

[dependabot]

Bumps spiffe/spire-server from 1.15.0 to 1.15.1.

You can trigger a rebase of this PR by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR:

• @dependabot rebase will rebase this PR
• @dependabot recreate will recreate this PR, overwriting any edits that have been made to it
• @dependabot show <dependency name> ignore conditions will show all of the ignore conditions of the specified dependency
• @dependabot ignore this major version will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this minor version will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself)
• @dependabot ignore this dependency will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself)

Note
Automatic rebases have been disabled on this pull request as it has been open for over 30 days.

[github-actions]

Thanks for opening your first ProtocolSoup pull request.

Pick the validation checks from the PR template that match your change. Use git commit -s for DCO sign-off when you can—if you forgot, comment and maintainers will help before merge (there is no bot that blocks the PR for this alone).

Helpful links:

• PR workflow: https://docs.protocolsoup.com/developers/pull-request-workflow/
• Development setup: https://docs.protocolsoup.com/developers/development-setup/
• Add a protocol: https://docs.protocolsoup.com/developers/extending/add-a-protocol/

[dependabot]

A newer version of spiffe/spire-server exists, but since this PR has been edited by someone other than Dependabot I haven't updated it. You'll get a PR for the updated version as normal once this PR is merged.

[dependabot]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version. You can also ignore all major, minor, or patch releases for a dependency by adding an ignore condition with the desired update_types to your config file.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.