[FIX] tools: raise validation error while invalid expression

When the user tries to modify the view with an invalid xpath expression,
an XPathSyntaxError traceback will appear.

Steps to produce:
1. Install the Accounting module.
2. Settings > Technical > UI > Views > Open any view
3. Invalidate expr syntax and try to save, thus an error will be generated.

Error: XPathSyntaxError: Invalid expression

This commit handles XPathSyntaxError by raising ValidationError
instead of a traceback.

sentry-4377014622

closes odoo/odoo#136523

X-original-commit: a0cf5d9d
Signed-off-by: Achraf Ben Azzouz (abz) <abz@odoo.com>