Handle old migration format

lib/mix/tasks/migrate.ex

@@ -34,7 +34,7 @@ defmodule Mix.Tasks.Archethic.Migrate do
 
     migrations_to_run =
       if File.exists?(migration_file_path) do
-        File.read!(migration_file_path) |> filter_migrations_to_run(function)
+        read_file(migration_file_path) |> filter_migrations_to_run(function)
       else
         # File does not exist when it's the first time the node is started
         # We create the folder to write the migration file on first start
@@ -99,4 +99,17 @@ defmodule Mix.Tasks.Archethic.Migrate do
     :code.delete(module)
     :code.purge(module)
   end
+
+  defp read_file(path) do
+    # handle old migration file format
+    file_content = File.read!(path)
+
+    if String.contains?(file_content, ";") do
+      last_version = file_content |> String.split(";") |> Enum.reject(&(&1 == "")) |> List.last()
+      File.write(path, last_version)
+      last_version
+    else
+      file_content
+    end
+  end
 end