[FIX] core: incomplete traceback

XML loading always raises a ParseError, however when an XML loading error is triggered from an HTTP request (e.g. a button) the final ParseError logged & shown to the user would not be properly chained to its ancestor, leading the original cause to be lost and issues being much harder to diagnose.

This cause is lost in _handle_exception where we duplicate the exception in order to chain it correctly, the __cause__ of the source exception was not properly copied over, and would thus break the chain.

The fix also requires explicitly chaining the ParseError to its cause, this should not be necessary but the cause is also lost if this is missing, it is not clear why.

opw-2381776

closes odoo/odoo#61914

Signed-off-by: Xavier Morel (xmo) <xmo@odoo.com>