Change order of actions in migration upgrade guide

Author: PostScripton

docs/upgrade/3.x_to_4.x.md

@@ -44,6 +44,12 @@ private const TABLES = [
 public function up(): void
 {
     foreach (self::TABLES as $tableName => $columns) {    
+        Schema::table($tableName, function (Blueprint $table) use ($columns) {
+            foreach ($columns as $column) {
+                $table->bigInteger($column)->default(0)->change();
+            }
+        });
+    
         $lackingDecimalPlaces = 4 - self::DECIMALS;
         if ($lackingDecimalPlaces > 0) {
             $multiplier = 10 ** $lackingDecimalPlaces;
@@ -56,12 +62,6 @@ public function up(): void
                         ->toArray()
                 );
         }
-
-        Schema::table($tableName, function (Blueprint $table) use ($columns) {
-            foreach ($columns as $column) {
-                $table->bigInteger($column)->default(0)->change();
-            }
-        });
     }
 }
 ```