[tests] Add missing sample_config admin tests on 1.1

[asmodehn]

Checklist

• I have read the OpenWISP Contributing Guidelines.
• I have manually tested the changes proposed in this pull request.
• I have written new test cases for new code and/or updated existing tests for changes to existing code.
• I have updated the documentation.

Description of Changes

This PR adds tests that seemed to be missing among the sample_config tests

This is currently a draft to check tests behaviour in the pipeline, using 1.1 as my current setup.
I plan to rebase on master later on.

[nemesifier]

Great work @asmodehn, I see only 1 failing test in the build:

FAIL: test_device_with_config_change_deactivate_deactivate (openwisp2.sample_config.tests.TestTransactionAdmin)
This test checks the following things
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/unittest/case.py", line 59, in testPartExecutor
    yield
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/unittest/case.py", line 592, in run
    self._callTestMethod(testMethod)
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/unittest/case.py", line 550, in _callTestMethod
    method()
  File "/home/runner/work/openwisp-controller/openwisp-controller/openwisp_controller/config/tests/test_admin.py", line 2116, in test_device_with_config_change_deactivate_deactivate
    self.assertContains(
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/site-packages/django/test/testcases.py", line 466, in assertContains
    self.assertEqual(
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/unittest/case.py", line 837, in assertEqual
    assertion_func(first, second, msg=msg)
  File "/opt/hostedtoolcache/Python/3.9.21/x64/lib/python3.9/unittest/case.py", line 830, in _baseAssertEqual
    raise self.failureException(msg)
AssertionError: 23 != 22 : Found 23 instances of '<div class="readonly">' in response (expected 22)

[nemesifier]

Handled the 1.1 branch manually after merging #996 in 5e1a105, thanks @asmodehn!