Revert "Correct Models Unit and Category"

This reverts commit 45702aa4f2.

Francesco.Recipes.World/Models/BackendModels/Category/Category.cs

@@ -4,7 +4,7 @@
     public class Category
     {
         public Guid Id { get; set; }
-        public string Name { get; set; }
+        public string? Name { get; set; }
         public virtual ICollection<Recipe> Recipes { get; set; } = new List<Recipe>();
     }
 }

Francesco.Recipes.World/Models/BackendModels/Unit/Unit.cs

@@ -7,8 +7,8 @@ namespace Francesco.Recipes.World.Models.BackendModels.Unit
     public class Unit
     {
         public Guid Id{ get; set; }
-        public string Name { get; set; }
-        public string Symbol { get; set; }
+        public string? Name { get; set; }
+        public string? Symbol { get; set; }
         public virtual ICollection<RecipeIngredient> RecipeIngredient { get; set; } = new List<RecipeIngredient>();
     } 
 }