buffer_cache/texture_cache: Make GC functions private

src/video_core/texture_cache/texture_cache.h

@@ -110,9 +110,6 @@ public:
     /// Notify the cache that a new frame has been queued
     void TickFrame();
 
-    /// Runs the Garbage Collector.
-    void RunGarbageCollector();
-
     /// Return a constant reference to the given image view id
     [[nodiscard]] const ImageView& GetImageView(ImageViewId id) const noexcept;
 
@@ -207,6 +204,9 @@ private:
         }
     }
 
+    /// Runs the Garbage Collector.
+    void RunGarbageCollector();
+
     /// Fills image_view_ids in the image views in indices
     void FillImageViews(DescriptorTable<TICEntry>& table,
                         std::span<ImageViewId> cached_image_view_ids, std::span<const u32> indices,