Fix psa arch test refspec

The PSA Arch test upstream project has renamed the 'master' branch
to 'main'. The refspec in the TS external component is updated
in-line with this change.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Signed-off-by: Gyorgy Szing <Gyorgy.Szing@arm.com>
Change-Id: I3a76711f086cb56968e05dd804c5d9121ace624a
1 file changed