gaia-dpci/GaiaXPy: GaiaXPy 1.2.4

Fixed problem in the application of the flux offset for the standardised system PanSTARRS1 (PhotometricSystem.PanSTARRS1_Std). The flux offset is part of the standardisation process described in Section 2.2.1 and equation 13 in Gaia Collaboration, Montegriffo, et al., 2022. In previous versions no flux offset was applied to the flux. Flux error and magnitude were derived consistently. Replaced SDSS filters (available as PhotometricSystem.SDSS) with those defined in Doi et al. 2010, AJ, 141, 47. Note that the standardised version (PhotometricSystem.SDSS_Std) was already based on Doi et al. 2010, AJ, 141, 47 and is therefore unchanged with respect to previous versions of GaiaXPy