Run the i18n workflow when the i18n workflow itself changes

Its `paths` filter listed `i18n/**` but not the workflow file, so a change to the
workflow - an action bump, say - triggered nothing. Those bumps automerge on a
branch, so they were merging with nothing having run them.

The Molecule workflow already lists itself for this reason. `update-translations.yml`
cannot do the same: it only runs on pushes to master, and it holds `contents: write`
and `pull-requests: write` to open translation PRs, so running it from a dependency
branch would be worse than not exercising it. Its bumps stay unexercised on purpose,
and a broken one shows up as a failed translations run rather than as anything users
see.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SEH3vxYSQ5SV4N5z61eyGT

.github/workflows/i18n.yml

@@ -12,9 +12,11 @@ on:  # yamllint disable-line rule:truthy
   push:
     paths:
       - "i18n/**"
+      - ".github/workflows/i18n.yml"
   pull_request:
     paths:
       - "i18n/**"
+      - ".github/workflows/i18n.yml"
   workflow_dispatch:
 
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