Updating API version (#1892)

Updated API version + Added copyright declaration in the newly
introduced `.bazelversion` file.

.bazelversion

@@ -1 +1,14 @@
 6.1.0
+# Copyright 2023 The StableHLO Authors. All Rights Reserved.
+#
+# Licensed 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
+#
+#      https://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.

stablehlo/api/PortableApi.h

@@ -27,7 +27,7 @@ namespace stablehlo {
 
 /// Return the current version for portable API.
 /// Increments on all meaningful changes to this file.
-inline int64_t getApiVersion() { return 4; }
+inline int64_t getApiVersion() { return 5; }
 
 // Get the current StableHLO version.
 //