Fixed cancel action on snippet edit form

What does this MR do?

The MR fixes the href attribute of the "Cancel" button on Snippet Edit Form (Vue application). Previously, the action always redirected to the list of all snippets (project or personal ones) when clicked. This MR fixes this for existing snippets and redirects to the snippet view instead of the listing of all snippets.

To test, you need to enable the feature flag (:snippet_edit_vue) locally.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team