Avoid reinstalling bundler if the required version is already installed

Author: ntkme

bundler.js

@@ -144,7 +144,10 @@ export async function installBundler(bundlerVersionInput, rubygemsInputSet, lock
   const versionParts = [...bundlerVersion.matchAll(/\d+/g)].length
   const bundlerVersionConstraint = versionParts >= 3 ? bundlerVersion : `~> ${bundlerVersion}.0`
 
-  await exec.exec(gem, ['install', 'bundler', '-v', bundlerVersionConstraint])
+  // Use --conservative only when installing a percise version.
+  const conservative = versionParts >= 3 ? ['--conservative'] : []
+
+  await exec.exec(gem, ['install', 'bundler', '-v', bundlerVersionConstraint, ...conservative])
 
   return bundlerVersion
 }