[infra] Add a Debug-All-NativeFonts GPU job on 10.15

...since the other Debug-All-NativeFonts GPU job is on a different GPU
and CPU ISA.

Add an "i5" extraConfig option so we can distinguish between the 2
differently-CPU'd MacMini7,1s.

Change-Id: I609d5361c313a005d888ca7a847375cad78dec01
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/506778
Reviewed-by: Ben Wagner <bungeman@google.com>
3 files changed