Fix byte to float color conversion in DisplayServerWindows::screen_get_pixel

[kleonc]

255 should be mapped to 1.0, it was mapped to 255.0 / 256.0.

byte / 255.0 is how we convert in most places I think (e.g. in Color or Image).

Fixes #79348.

No incorrect conversion spotted for Linux / MacOS:

godot/platform/linuxbsd/x11/display_server_x11.cpp

Line 1220 in 23318e8

return Color(float(c.red) / 65535.0, float(c.green) / 65535.0, float(c.blue) / 65535.0, 1.0);

godot/platform/macos/display_server_macos.mm

Lines 2226 to 2228 in 23318e8

	CGFloat components[4];
	[color getRed:&components[0] green:&components[1] blue:&components[2] alpha:&components[3]];
	return Color(components[0], components[1], components[2], components[3]);

[aaronfranke]

Yes, it should divide by 255 as this PR does.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.2.