[TECH DEBT] Let LinterContext.linter return None if no linter is found instead of raising a ValueError

[JCZuurmond]

Description

Let LinterContext.linter return None if no linter is found instead of raising a ValueError:

ucx/src/databricks/labs/ucx/source_code/linters/context.py

Lines 105 to 112 in f47722c

	def linter(self, language: Language) -> Linter:
	if language not in self._linters:
	raise ValueError(f"Unsupported language: {language}")
	if language is Language.PYTHON:
	return PythonSequentialLinter(cast(list[PythonLinter], self._linters[language]), [], [])
	if language is Language.SQL:
	return SqlSequentialLinter(cast(list[SqlLinter], self._linters[language]), [], [])
	raise ValueError(f"Unsupported language: {language}")

Motivation

For a more graceful way handling of a linter not being found, now we are unsure if the last ValueError will be raised in case someone adds a new linter for a new language but forgets to update the if condition there