Fix #145590: translations causing driver expressions to fail

Resolve regression in [0] where name was translated for the name but
not the Python expressions, it's possible to translate both but this
doesn't seem so simple as these functions don't necessarily run at
the same time.

[0]: 6926596174

source/blender/blenkernel/intern/fcurve_driver.cc

@@ -1020,14 +1020,13 @@ DriverVar *driver_add_new_variable(ChannelDriver *driver)
   dvar = MEM_callocN<DriverVar>("DriverVar");
   BLI_addtail(&driver->variables, dvar);
 
+  /* Don't use translations as this is referenced as a literal in #ChannelDriver::expression. */
+  const char *name_default = "var";
+
   /* Give the variable a 'unique' name. */
-  STRNCPY_UTF8(dvar->name, CTX_DATA_(BLT_I18NCONTEXT_ID_ACTION, "var"));
-  BLI_uniquename(&driver->variables,
-                 dvar,
-                 CTX_DATA_(BLT_I18NCONTEXT_ID_ACTION, "var"),
-                 '_',
-                 offsetof(DriverVar, name),
-                 sizeof(dvar->name));
+  STRNCPY_UTF8(dvar->name, name_default);
+  BLI_uniquename(
+      &driver->variables, dvar, name_default, '_', offsetof(DriverVar, name), sizeof(dvar->name));
 
   /* Set the default type to 'single prop'. */
   driver_change_variable_type(dvar, DVAR_TYPE_SINGLE_PROP);