linux-capture: Request at least 8 bits for alpha

10bpc support is under active development all over the linux stack
so while we wait for it to mature, request an alpha size of 8.

plugins/linux-capture/xcompcap-main.cpp

@@ -400,6 +400,7 @@ void XCompcapMain::updateSettings(obs_data_t *settings)
 		GLX_BIND_TO_TEXTURE_RGBA_EXT, GL_TRUE,
 		GLX_DRAWABLE_TYPE, GLX_PIXMAP_BIT,
 		GLX_BIND_TO_TEXTURE_TARGETS_EXT, GLX_TEXTURE_2D_BIT_EXT,
+		GLX_ALPHA_SIZE, 8,
 		GLX_DOUBLEBUFFER, GL_FALSE,
 		None
 	};