fix(pre-commit): use correct stages syntax for manual hooks

`manual: true` is not valid pre-commit syntax and gets silently
ignored, causing oca-gen-addon-readme and oca-gen-external-dependencies
to run in CI. The README hook then fails due to platform-dependent
docutils table rendering differences between Ubuntu (CI) and macOS.

Replace with `stages: [manual]` which is the correct pre-commit way
to exclude hooks from normal runs.

Author: emjay0921

.pre-commit-config.yaml

@@ -60,9 +60,9 @@ repos:
           - --if-source-changed
           - --keep-source-digest
           - --convert-fragments-to-markdown
-        manual: true
+        stages: [manual]
       - id: oca-gen-external-dependencies
-        manual: true
+        stages: [manual]
       - id: oca-gen-addons-table
   - repo: https://github.com/OCA/odoo-pre-commit-hooks
     rev: v0.1.7