Correctly raise GitlabHeadError in head method

## Description of the problem, including code/CLI snippet

GitlabHeadError should be raised in https://github.com/python-gitlab/python-gitlab/blob/main/gitlab/v4/objects/files.py#L140

## Expected Behavior

GitlabHeadError

## Actual Behavior

GitlabHttpError

## Specifications

  - python-gitlab version: v4.12.1
