Fix Run1 PixelDigitization legacy configuration (ATLASSIM-6962)
Output differences were observed between Run1 Pixel Digitization in ART jobs when using legacy and CA-based configuration. This was tracked down to fixes in !41985 (merged) and !45942 (merged) which were only applied to CA-based configuration, but until recently the Run1 Digitization ART jobs only used legacy configuration so the discrepancy was not spotted at the time.
Closes ATLASSIM-6962