TST: Decoupled more xlrd reading tests from openpyxl
- [X] closes #27111
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

@simonjayhawkins 
This PR results in an additional 2 warnings. although 8 of the same were introduced in #25092.

```
pandas/tests/io/excel/test_readers.py::TestReaders::test_reader_special_dtypes[openpyxl-.xlsx]
pandas/tests/io/excel/test_readers.py::TestReaders::test_reader_special_dtypes[openpyxl-.xlsm]
pandas/tests/io/excel/test_readers.py::TestReaders::test_reading_all_sheets[openpyxl-.xlsx]
pandas/tests/io/excel/test_readers.py::TestReaders::test_reading_all_sheets[openpyxl-.xlsm]
pandas/tests/io/excel/test_readers.py::TestReaders::test_reading_multiple_specific_sheets[openpyxl-.xlsx]
pandas/tests/io/excel/test_readers.py::TestReaders::test_reading_multiple_specific_sheets[openpyxl-.xlsm]
pandas/tests/io/excel/test_readers.py::TestReaders::test_read_excel_squeeze[openpyxl-.xlsx]
pandas/tests/io/excel/test_readers.py::TestReaders::test_read_excel_squeeze[openpyxl-.xlsm]
pandas/tests/io/excel/test_readers.py::TestExcelFileRead::test_excel_passes_na[openpyxl-.xlsx]
pandas/tests/io/excel/test_readers.py::TestExcelFileRead::test_excel_passes_na[openpyxl-.xlsm]
  C:\Users\simon\Anaconda3\envs\pandas-dev\lib\site-packages\openpyxl\worksheet\_reader.py:296: UserWarning: Unknown extension is not supported and will be removed
    warn(msg)
``` @simonjayhawkins that should be solved by https://github.com/pandas-dev/pandas/pull/27122