Panic occurs when formatting with separator and some format specifier (#6213)

* Fix get_separator_interval

* Add extra tests

* Remove FormatType::Number from match arm

extra_tests/snippets/builtin_format.py

@@ -188,6 +188,11 @@ assert f"{12.34 + 5.6j:^30E}" == "  1.234000E+01+5.600000E+00j  "
 assert f"{12345.6 + 7890.1j:,}" == "(12,345.6+7,890.1j)"
 assert f"{12345.6 + 7890.1j:_.3f}" == "12_345.600+7_890.100j"
 assert f"{12345.6 + 7890.1j:>+30,f}" == "  +12,345.600000+7,890.100000j"
+assert f"{123456:,g}" == "123,456"
+assert f"{123456:,G}" == "123,456"
+assert f"{123456:,e}" == "1.234560e+05"
+assert f"{123456:,E}" == "1.234560E+05"
+assert f"{123456:,%}" == "12,345,600.000000%"
 
 # test issue 4558
 x = 123456789012345678901234567890