fix(python): proscribe multiline assignments

[jorpic]

This fixes aws/jsii#3968 by disallowing line breaks before regularCallExpression and newExpression.

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[jorpic]

The testsuite fails because mocking fs.*Sync methods is broken on node 20.8. (tschaub/mock-fs#380).

mock-fs is used in tests to create a fake file

jsii-rosetta/test/jsii/assemblies.test.ts

Lines 203 to 206 in 9f271e6

	test('Backwards compatibility with literate integ tests', async () => {
	mockfs({
	'/package/test/integ.example.lit.ts': '# Some literate source file',
	});

which then should be read in

jsii-rosetta/src/fixtures.ts

Lines 47 to 53 in 9f271e6

	function loadLiterateSource(directory: string, literateFileName: string) {
	const fullPath = path.join(directory, literateFileName);
	const exists = fs.existsSync(fullPath);
	if (!exists) {
	// This couldn't really happen in practice, but do the check anyway
	throw new Error(`Sample uses literate source ${literateFileName}, but not found: ${fullPath}`);
	}

but this fails due to the mock-fs issue.