[isaacroldan]

Description

This is part of the gardener cleanup. On 2026-10-30 Isaac decided to remove the gardener Slack notifications.

• Problem: gardener-notify-event.yml and gardener-notify-slack.yml labelled every new issue and PR devtools-gardener and posted each one to #devtools-gardener-backlog. Each post was a bare linked title, and together they made up most of the channel's noise.
• Change: this PR deletes both workflows, which also removes the auto-labelling of every new issue and PR as devtools-gardener. From now on, the Mission Control gardener hub or a Torrent routine will surface new issues and Dependabot PRs.
• Impact: CI/automation only, with no gem changes. Nothing else in the repo depends only on these two workflows. I grepped for gardener-notify, GARDENER_SLACK, SLACK_GARDENER and devtools-gardener and checked helper scripts, label/config files and docs. This PR doesn't touch the devtools-gardener label, the other workflows or the Mission Control hub.

Secrets and variables these workflows used (none are deleted here; removing them is left to the maintainers):

• secrets.SLACK_GARDENER_BOT_TOKEN: still used on main by gardener-investigate-issue.yml, which Remove unused gardener workflows, Slack notifications and auto-labelling #1474 removes. Once both PRs merge, nothing in the repo uses it.
• vars.GARDENER_SLACK_CHANNEL_ID: same as above (gardener-investigate-issue.yml, removed in Remove unused gardener workflows, Slack notifications and auto-labelling #1474).

Related: #1474 (earlier gardener cleanup that removes gardener-investigate-issue.yml and fixes the waiting-for-response closer).

How has this been tested?

There's no code to test because this only deletes workflows. After merge, opening an issue or PR should no longer run Gardener - Notify Event / Gardener - Notify Slack, add devtools-gardener, or post to Slack. Because the notify workflows run via pull_request_target from main, opening this PR posts it to #devtools-gardener-backlog one last time.

Checklist:

• My commit message follow the pattern described in here
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.: not applicable
• I have updated the project documentation.: not needed
• I have added a changelog line.: not user-facing, no entry