Check for gh tool during sanity checks

Add a sanity check to verify that the GitHub CLI (gh) tool is available
in PATH before proceeding with the release. This prevents the release
process from failing late in the process when gh is needed for creating
PRs in vendor repositories.

Fixes #1433

Generated-by: Claude Opus 4.5

Author: j-rivero

release.py

@@ -412,6 +412,13 @@ def sanity_check_bump_linux(source_tarball_uri):
               'to call builders and not source generation')
 
 
+def sanity_check_gh_tool():
+    if shutil.which('gh') is None:
+        error("The 'gh' (GitHub CLI) tool is required but was not found in PATH.\n"
+              "Please install it from: https://cli.github.com/")
+    print_success("GitHub CLI (gh) tool is available")
+
+
 def sanity_checks(args, repo_dir):
     print("Safety checks:")
     sanity_package_name_underscore(args.package, args.package_alias)
@@ -431,6 +438,7 @@ def sanity_checks(args, repo_dir):
             sanity_check_cmake_version(args.package, args.version)
         sanity_project_package_in_stable(args.version, args.upload_to_repository)
 
+    sanity_check_gh_tool()
     check_credentials(args.auth_input_arg)
     print_success("Jenkins credentials are good")
     shutil.rmtree(repo_dir)