Update SafeRedirectMixin

[mortenlyn]

Can we check that this fixes the issue the github-advanced-security bot found without pushing it?

[Copilot]

Pull Request Overview

This PR updates the SafeRedirectMixin to improve URL validation and security by enhancing the handling of redirect URLs. The changes focus on making the redirect logic more robust and preventing potential security vulnerabilities.

• Enhanced URL extraction with proper string validation and trimming
• Improved parameter handling to avoid duplicate URL extraction
• Added comprehensive documentation for all methods

[Copilot]

The isinstance check is redundant since request.POST.get() and request.GET.get() always return strings or None. Consider removing this check or handle the case where next_url could be a list (if multiple values are provided for the same parameter).

Suggested change

	if isinstance(next_url, str):
	if isinstance(next_url, list):
	next_url = next_url[0] # Extract the first value if multiple are provided
	if next_url:

[Copilot]

[nitpick] The explicit 'url=' parameter name is unnecessary here since it's the first positional parameter of url_has_allowed_host_and_scheme. This change makes the code less consistent with the original implementation.

Suggested change

	url=next_url,
	next_url,