Fixed typo introduce when building PhpSettingsSource due to
copy-paste of boiler plate class code.
Change-Id: I013ebc5a3b041187a3aa312498140fa40c235fbf
This is an intermediate step before converting the merge strategies or
other configs/config schemas to YAML.
Bug: T297320
Change-Id: I91cd04d14f0ff86125fc8870984dab045c2098b5