**Steps to Reproduce:**
- Create a new database.
- Install any module (for example, Payroll).
- Go to Settings → Technical → Security → Groups.
- Open any group and assign an inherited view in the Views section.
- Upgrade the module.

**Issue:**
- Odoo already prevents assigning groups directly on inherited view records in
ir.ui.view. However, it is still possible to indirectly assign groups to
inherited views through res.groups via the view_access relation.

- This creates entries in ir_ui_view_group_rel and can trigger a ValidationError
during module upgrades. As a result, users may unknowingly create invalid
group-view relations, leading to errors and confusion.

**Solution:**
- Add a validation constraint on res.groups to prevent linking groups to
  inherited views via the view_access relation.

- Raise a ValidationError when such an assignment is attempted, with the message:
  "Groups should instead be defined using the 'groups' attribute inside the view XML definition."

This ensures that inherited views cannot be assigned to groups,
avoiding invalid configurations and preventing errors during module upgrades.

**opw-6015526**

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Forward-Port-Of: odoo/odoo#254849

…r rejections

Yahoo and other strict mail servers reject emails with folded Subject headers containing RFC 2047 encoded-words when the folding occurs at inappropriate positions, resulting in "554 Invalid Subject header" errors.

The root cause is in Python's stdlib (bpo-144156). In an ideal world we would be fixing the issue there, but experience tells us that they are very slow to fix bugs / merge PRs in the email module, and even when they do they usually don't backport the fixes in the python versions we use.

This commit extends the existing IdentificationFieldsNoFoldPolicy to also prevent Subject header folding, keeping long subjects on a single line (up to 998 characters per RFC 5322 "MUST" requirement, from the 98 "SHOULD" limit). Since at it, include the other "user defined" smtp headers: to, from, ...

The solution follows the same pattern already established for identification headers (Message-ID, In-Reply-To, References) where Odoo prevents folding to avoid MTAs rewriting these critical headers and breaking email threading.

closes odoo/odoo#250388

See-also: #243119
Backport: #247057

Forward-Port-Of: odoo/odoo#254670