gateway: bump dawidd6/action-send-mail from 3.12.0 to 6

Bumps [dawidd6/action-send-mail](https://github.com/dawidd6/action-send-mail) from 3.12.0 to 6.
- [Release notes](https://github.com/dawidd6/action-send-mail/releases)
- [Commits](dawidd6/action-send-mail@2cea961...6d98ae3)

---
updated-dependencies:
- dependency-name: dawidd6/action-send-mail
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/dummy.yml

@@ -32,7 +32,7 @@ jobs:
       - uses: crazy-max/ghaction-import-gpg@e89d40939c28e39f97cf32126055eeae86ba74ec  # v6.3.0
       - uses: crazy-max/ghaction-setup-docker@b60f85385d03ac8acfca6d9996982511d8620a19  # v4
       - uses: damccorm/tag-ur-it@6fa72bbf1a2ea157b533d7e7abeafdb5855dbea5
-      - uses: dawidd6/action-send-mail@2cea9617b09d79a095af21254fbcb7ae95903dde  # v3.12.0
+      - uses: dawidd6/action-send-mail@6d98ae34d733f9a723a9e04e94f2f24ba05e1402  # v6
       - uses: docker://jekyll/jekyll@sha256:400b8d1569f118bca8a3a09a25f32803b00a55d1ea241feaf5f904d66ca9c625
       - uses: dominikh/staticcheck-action@4ec9a0dff54be2642bc76581598ba433fd8d4967  # v1.1.0
       - uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36  # v3.0.2