Renaming bswap_tests test case so that the name does not collide with the test suite name

Summary:
This is the only test where the suite and test names are the same. It results in
strange <no class> output in the Teamcity UI: https://build.bitcoinabc.org/viewLog.html?currentGroup=class&scope=Bitcoin_ABC_unit_tests%23teamcity%23*%23teamcity%23*&pager.currentPage=1&order=NAME_ASC&recordsPerPage=20&filterText=&status=&buildTypeId=BitcoinABCMasterLinux&buildId=29086&tab=testsInfo

Test Plan: Check that CI shows bswap_tests class name correctly with this patch

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D6982