Remove GET based actions that make server side changes.

[gojo-satorou-v7]

Below are the actions identified by coderabbit, check first if it's really an issue or just false positive. Check #4057 for more info.

I've identified several endpoints that modify server-side state in response to GET requests, which could lead to CSRF vulnerabilities.

Here are the specific problematic functions:

In website/views/issue.py:
    like_issue(request, issue_pk) - modifies user upvotes
    dislike_issue(request, issue_pk) - modifies user downvotes
    flag_issue(request, issue_pk) - modifies issue flags
    save_issue(request, issue_pk) - adds/removes saved issues
    unsave_issue(request, issue_pk) - removes saved issues

In website/views/organization.py:
    like_activity(request, id) - modifies activity likes/approval
    dislike_activity(request, id) - modifies activity dislikes
    approve_activity(request, id) - changes approval status

None of these functions check for the request method, meaning they process changes via GET requests.