File name conflicts on case-insensitive filesystems

[cfxegbert]

The default filesystem on MacOS is case-insensitive but has case preserving file names. If the test generation has arguments that just differ in case a case-insensitive file name conflict may happen. This happens on eza with

• ptest_tests_test_dir_-l_--sort_Ext.toml => ptest_tests_test_dir_-l_--sort_ext.toml
• ptest_tests_test_dir_-l_--sort_Name.toml => ptest_tests_test_dir_-l_--sort_name.toml
• ptest_tests_test_dir_-l_--sort_Extension.toml => ptest_tests_test_dir_-l_--sort_extension.toml
• ptest_tests_test_dir_-l_--sort_Filename.toml => ptest_tests_test_dir_-l_--sort_filename.toml
• ptest_tests_test_dir_-l_-s_Ext.toml => ptest_tests_test_dir_-l_-s_ext.toml
• ptest_tests_test_dir_-l_-s_Extension.toml => ptest_tests_test_dir_-l_-s_extension.toml
• ptest_tests_test_dir_-l_-s_Filename.toml => ptest_tests_test_dir_-l_-s_filename.toml
• ptest_tests_test_dir_-l_-s_Name.toml => ptest_tests_test_dir_-l_-s_name.toml

[cafkafk]

Should be solved by #9