Remove BuilddBaseAlias string-match guard in handle_runtime_error

[tonyandrewmeyer]

craft_application/util/logging.py (lines ~115-133, introduced in #1082) catches
the bare ValueError("'X.YY' is not a valid BuilddBaseAlias") from craft-providers
by string-matching the message:

case ValueError() if "BuilddBaseAlias" in str(error):

This is a shallow guard. The proper fix is for craft-providers to raise a typed
error at the lookup site; once that lands, this match arm should be replaced by
a typed except clause (or removed if the upstream handler covers it).

Blocked by: canonical/craft-providers#969