chore: use baseBranch instead of hardcoded master

Author: alucardzom

.github/scripts/stable-sync.js

@@ -103,7 +103,7 @@ async function runGitCommands() {
       console.log('Executing extension-specific commands...');
 
       const { stdout: packageJsonContent } = await exec(
-        'git show origin/master:package.json',
+        `git show origin/${baseBranch}:package.json`,
       );
       const packageJson = JSON.parse(packageJsonContent);
       const packageVersion = packageJson.version;