Don't rebuild existing fiscal years

This would happen when running tests on a DB where ``account_period`` is
already installed.

Follow-up on rev e9cc0fe9ab5f.

__manifest__.py

@@ -22,7 +22,7 @@
     "name": "Accounting Periods",
     "license": "AGPL-3",
     "summary": "Add period accounting concept",
-    "version": "13.0.1.2.0",
+    "version": "13.0.1.2.1",
     "category": "Accounting/Accounting",
     "author": "XCG Consulting",
     "website": "https://odoo.consulting/",

models/account_chart_template.py

@@ -56,6 +56,11 @@
         )
         year_str = str(end_date.year)
 
+        if self.env["account.fiscalyear"].search(
+            [("code", "=", year_str)], limit=1
+        ):
+            return  # Fiscal year already exists in this company.
+
         self.env["account.fiscalyear"].create(
             {
                 "code": year_str,