Fix licence info in signals.pl

File header does not contain any actual license, it's just an internal
joke. Fixed it and switch to formal Apache 2.0 License.

(cherry picked from commit 89b0544dff49e5ceed7b84662cf91bae94d37754)

src/test/mdb_admin/t/signals.pl

diff --git a/src/test/mdb_admin/t/signals.pl b/src/test/mdb_admin/t/signals.pl
index a11db27..319c007 100644
--- a/src/test/mdb_admin/t/signals.pl
+++ b/src/test/mdb_admin/t/signals.pl
@@ -1,5 +1,19 @@
-
-# Copyright (c) 2024-2024, MDB, Mother Russia
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
 
 # Minimal test testing streaming replication
 use strict;
@@ -71,4 +85,4 @@
 
 # print ($res_reg_lh_2, $stdout_reg_lh_2, $stderr_reg_lh_2, "\n");
 
-done_testing();
\ No newline at end of file
+done_testing();