Merge pull request #1810 from Unity-Technologies/FixTextureCacheMipmapWarningForPlanarReflection

Fixed TextureCache2D mipmap check for RenderTextures

com.unity.render-pipelines.core/CoreRP/Textures/TextureCache.cs

 
         bool TextureHasMipmaps(Texture texture)
         {
-            var crt = texture as CustomRenderTexture;
-
-            else if (crt is CustomRenderTexture)
-                return ((CustomRenderTexture)texture).useMipMap;
+            else if (texture is RenderTexture)
+                return ((RenderTexture)texture).useMipMap;
             return false;
         }