[WebGPU] RenderBundleEncoder::setVertexBuffer may result in a UAF

https://bugs.webkit.org/show_bug.cgi?id=274525
<radar://128537945>

Reviewed by Dan Glastonbury.

Every other call site to recordCommand captures by Ref, this
was the only outlier passing a raw C++ pointer to the lambda.

* Source/WebGPU/WebGPU/RenderBundleEncoder.mm:
(WebGPU::RenderBundleEncoder::setVertexBuffer):

Canonical link: https://commits.webkit.org/279171@main

Source/WebGPU/WebGPU/RenderBundleEncoder.mm

@@ -1076,8 +1076,8 @@ - (instancetype)initWithICB:(id<MTLIndirectCommandBuffer>)icb pipelineState:(id<
         }
 
         m_requiresMetalWorkaround = false;
-        recordCommand([slot, optionalBuffer, offset, size, protectedThis = Ref { *this }] {
-            protectedThis->setVertexBuffer(slot, optionalBuffer, offset, size);
+        recordCommand([slot, optionalBuffer = RefPtr { optionalBuffer }, offset, size, protectedThis = Ref { *this }] {
+            protectedThis->setVertexBuffer(slot, optionalBuffer.get(), offset, size);
             return false;
         });
     }