release.sh: check that the next version doesn't equal to the current …

…one (#1582)

Motivation:

To prevent scenarios like #1580, let's enhance validation of input
parameter for the `release.sh` script.

Modifications:

- Compare passed next version with the current version from
`gradle.properties`, fails fast if they are equal;

Result:

Enhanced validation of next version parameter.

scripts/release.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 #
-# Copyright © 2019 Apple Inc. and the ServiceTalk project authors
+# Copyright © 2019, 2021 Apple Inc. and the ServiceTalk project authors
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -38,10 +38,18 @@ if ( echo "$nextVersion" | grep -qv "SNAPSHOT" ); then
     exit 1
 fi
 
-version=$(cat gradle.properties | grep version= |  sed 's/-SNAPSHOT//' | sed 's/^version=//')
+version=$(cat gradle.properties | grep version= | sed 's/^version=//')
+
+if [ "$nextVersion" == "$version" ]; then
+    echo "Next version '$nextVersion' cannot be equal to the current version in gradle.properties: $version"
+    usage
+    exit 1
+fi
+
+version=$(echo "$version" | sed 's/-SNAPSHOT//')
 
 if ( echo "$version" | grep -q "SNAPSHOT" ); then
-    echo "Expected release version to be a release version, not snapshot"
+    echo "Expected release version '$version' to be a release version, not a snapshot"
     usage
     exit 1
 fi