[RajGahoi]

Fixes #9747

Description

In \ViewSetMixin.as_view(), the \�ctions\ dictionary passed into the method was captured by the inner \�iew(request, *args, **kwargs)\ closure without being copied. During request dispatch, the block:
\\python
if 'get' in actions and 'head' not in actions:
actions['head'] = actions['get']
\
mutated the \�ctions\ dictionary in-place. This caused two problems:

1. The dictionary passed by the caller to \�s_view(actions)\ was mutated in-place.
2. \�iew.actions\ mutated after the first request was processed, leading to non-deterministic state between pre-request and post-request inspection.

Solution

• In \ViewSetMixin.as_view(), copy \�ctions\ via \�ctions = dict(actions)\ and populate the implicit 'head'\ mapping immediately at view creation time.
• Remove the in-place mutation logic from within the \�iew()\ closure.
• The caller's dictionary is preserved, and \�iew.actions\ is deterministic both before and after any request.

Testing

• Added unit tests in \ ests/test_viewsets.py\ covering:
  • Preserving caller's \�ctions\ dictionary without mutation.
  • Ensuring \�iew.actions\ contains 'head'\ deterministically before and after requests.
  • Preserving explicitly configured \head\ actions.
  • Ensuring viewsets without \get\ do not have \head\ added.
• Full test suite passed (1645 passed, 0 failed).
• Flake8 checks pass with 0 errors.