Fix missing closing bracket in checkout scmGit branches argument (#1723)

Author: ruyut

src/main/resources/jenkins/plugins/git/GitStep/help.html

@@ -19,7 +19,7 @@
     <p>
     The <code>git</code> step is a simplified shorthand for a subset of the more powerful <code>checkout</code> step:
 <pre>
-checkout scmGit(branches: [[name: 'main]],
+checkout scmGit(branches: [[name: 'main']],
     userRemoteConfigs: [[url: 'https://git-server/user/repository.git']])
 </pre>
     </p>

src/main/resources/jenkins/plugins/git/GitStep/help_ja.html

@@ -5,7 +5,7 @@
     <p>
         このステップは、一般的なSCMのステップである
 <pre>
-checkout scmGit(branches: [[name: 'main]],
+checkout scmGit(branches: [[name: 'main']],
     userRemoteConfigs: [[url: 'https://git-server/user/repository.git']])
 </pre>
     　　の短縮形です。