[IMP] web: force form view label font-size

Some labels may now be placed in a <h1,2,3> tag in some circumstances

addons/web/static/src/less/enterprise_compatibility.less

@@ -228,6 +228,10 @@ div.o_checkbox {
         width: auto!important; // oe_inline
     }
 
+    .oe_form label {
+        font-size: 13px;
+    }
+
     .o_form_field_many2manytags {
         .o-inline-flex-display();
         .o-flex-flow(row, wrap);