[FIX] base: round rates to 6 digits in currency kanban view

closes odoo/odoo#71531

Task: 2519395
X-original-commit: 6fc67b3682b88a6b45533702d286d73cb67c05ec
Signed-off-by: William André (wan) <wan@odoo.com>

odoo/addons/base/models/res_currency.py

@@ -84,7 +84,7 @@ class Currency(models.Model):
             currency.rate = (currency_rates.get(currency.id) or 1.0) / last_rate[company]
             currency.inverse_rate = 1 / currency.rate
             if currency != company.currency_id:
-                currency.rate_string = '1 %s = %s %s' % (company.currency_id.name, currency.rate, currency.name)
+                currency.rate_string = '1 %s = %.6f %s' % (company.currency_id.name, currency.rate, currency.name)
             else:
                 currency.rate_string = ''