It would be very helpful, to have an explicit data type "ArcGIS Pro projects" (e.g. "DEProProject") to use for GP parameters (including the special "CURRENT" keyword):
param = arcpy.Parameter("pro_project", "ArcGIS Pro Project", "Input", ==>"DEProProject"<==, "Required")
Currently the only workaround is to use the type "DEFile" and define the parameter filter list as shown below and using "CURRENT" as value:
param = arcpy.Parameter("pro_project", "ArcGIS Pro Project", "Input", "DEFile", "Required")
param.filter.list = ["", "aprx"]
param.value = "CURRENT"