Fix removing groups that have a slash in the name

[gary-kim]

Closes #18211

Fix removing groups that have a slash in the name such as /test.

I will backport manually once this is merged.

[gary-kim]

Should add some acceptance tests

EDIT: Oh, acceptance tests for this are currently disabled because of a needed patch?

server/tests/acceptance/features/users.feature

Lines 71 to 79 in 81b919e

	Scenario: create and delete a group
	Given I act as Jane
	And I am logged in as the admin
	And I open the User settings
	And I see that the list of users contains the user user0
	# disabled because we need the TAB patch:
	# https://github.com/minkphp/MinkSelenium2Driver/pull/244
	# And I assign the user user0 to the group Group1

@skjnldsv Do you think these could be reenabled now? Should probably be a different PR.

[skjnldsv]

@skjnldsv Do you think these could be reenabled now? Should probably be a different PR.

Highly doubt it, we're late by one major on selenium.
Too hard to upgrade.
We need to migrate our tests to cypress

[rullzer]

Needs a rebase

[gary-kim]

@rullzer Done