config: fix automatic names apply before schema upgrade

Each config reload on a node with old schema (less than 3.0.0) lead to
the error ER_SCHEMA_NEEDS_UPGRADE. This happened because the relevant
code didn't check for schema version before trying to apply the names.

Fix this.

Closes #9502

NO_DOC=bugfix
NO_CHANGELOG=fix in a not yet released behavior

src/box/lua/config/applier/box_cfg.lua

@@ -283,7 +283,9 @@ local function names_apply(config, missing_names, schema_version)
     names_alert_missing(config, missing_names)
     -- Don't wait for box.status to change, we may be already rw, set names
     -- on reload, if it's possible and needed.
-    names_try_set_missing()
+    if schema_version and schema_version >= mkversion.get_latest() then
+        names_try_set_missing()
+    end
 
     if names_state.is_configured then
         -- All triggers are already configured, nothing to do, but wait.

test/config-luatest/names_upgrade_test.lua

@@ -96,6 +96,12 @@ local function assert_before_upgrade()
     local info = box.info
     t.assert_equals(info.name, nil)
     t.assert_equals(info.replicaset.name, nil)
+    -- Check that config:reload() respects old schema version.
+    local config = require('config')
+    config:reload()
+    info = box.info
+    t.assert_equals(info.name, nil)
+    t.assert_equals(info.replicaset.name, nil)
 end
 
 local function assert_after_upgrade(instance_name, replicaset_name, names)