Be stricter on what's considered a scene path in CLI argument parsing
Be stricter on what's considered a scene path in CLI argument parsing

This closes #8721.

akien-mga/godot,MarianoGnu/godot,godotengine/godot,honix/godot,Paulloz/godot,godotengine/godot,sanikoyes/godot,firefly2442/godot,vkbsb/godot,pkowal1982/godot,akien-mga/godot,BastiaanOlij/godot,Shockblast/godot,BastiaanOlij/godot,Zylann/godot,Paulloz/godot,vkbsb/godot,BastiaanOlij/godot,josempans/godot,firefly2442/godot,vkbsb/godot,ex/godot,Shockblast/godot,sanikoyes/godot,Valentactive/godot,josempans/godot,josempans/godot,ex/godot,pkowal1982/godot,Valentactive/godot,vnen/godot,firefly2442/godot,ex/godot,guilhermefelipecgs/godot,pkowal1982/godot,akien-mga/godot,godotengine/godot,godotengine/godot,Valentactive/godot,MarianoGnu/godot,Zylann/godot,Zylann/godot,akien-mga/godot,guilhermefelipecgs/godot,guilhermefelipecgs/godot,sanikoyes/godot,vkbsb/godot,honix/godot,Shockblast/godot,vnen/godot,Faless/godot,firefly2442/godot,ZuBsPaCe/godot,BastiaanOlij/godot,MarianoGnu/godot,ZuBsPaCe/godot,Zylann/godot,honix/godot,guilhermefelipecgs/godot,ZuBsPaCe/godot,josempans/godot,firefly2442/godot,DmitriySalnikov/godot,pkowal1982/godot,Faless/godot,firefly2442/godot,Paulloz/godot,vnen/godot,honix/godot,ex/godot,Zylann/godot,Valentactive/godot,akien-mga/godot,pkowal1982/godot,MarianoGnu/godot,Zylann/godot,Faless/godot,Faless/godot,pkowal1982/godot,DmitriySalnikov/godot,DmitriySalnikov/godot,DmitriySalnikov/godot,Faless/godot,guilhermefelipecgs/godot,pkowal1982/godot,Valentactive/godot,ZuBsPaCe/godot,MarianoGnu/godot,sanikoyes/godot,sanikoyes/godot,BastiaanOlij/godot,vkbsb/godot,Shockblast/godot,vnen/godot,Faless/godot,Paulloz/godot,MarianoGnu/godot,ex/godot,vnen/godot,DmitriySalnikov/godot,akien-mga/godot,ex/godot,akien-mga/godot,BastiaanOlij/godot,MarianoGnu/godot,honix/godot,ex/godot,godotengine/godot,Shockblast/godot,Shockblast/godot,vnen/godot,Faless/godot,sanikoyes/godot,godotengine/godot,vnen/godot,sanikoyes/godot,guilhermefelipecgs/godot,josempans/godot,DmitriySalnikov/godot,vkbsb/godot,Faless/godot,vkbsb/godot,sanikoyes/godot,BastiaanOlij/godot,godotengine/godot,vnen/godot,akien-mga/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,josempans/godot,josempans/godot,honix/godot,Shockblast/godot,MarianoGnu/godot,guilhermefelipecgs/godot,pkowal1982/godot,godotengine/godot,firefly2442/godot,Valentactive/godot,Paulloz/godot,Shockblast/godot,ZuBsPaCe/godot,ZuBsPaCe/godot,Valentactive/godot,Valentactive/godot,ZuBsPaCe/godot,Zylann/godot,DmitriySalnikov/godot,BastiaanOlij/godot,Paulloz/godot,firefly2442/godot,vkbsb/godot,Zylann/godot,josempans/godot,Paulloz/godot,ex/godot