WebGLTextures: Fixed isXRRenderTarget check.

src/renderers/webgl/WebGLTextures.js

@@ -1593,7 +1593,7 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 
 					const glFormat = utils.convert( texture.format, texture.encoding );
 					const glType = utils.convert( texture.type );
-					const glInternalFormat = getInternalFormat( texture.internalFormat, glFormat, glType, texture.encoding, renderTarget.isXRRenderTarget );
+					const glInternalFormat = getInternalFormat( texture.internalFormat, glFormat, glType, texture.encoding, renderTarget.isXRRenderTarget === true );
 					const samples = getRenderTargetSamples( renderTarget );
 					_gl.renderbufferStorageMultisample( _gl.RENDERBUFFER, samples, glInternalFormat, renderTarget.width, renderTarget.height );