gemPush failed even $HOME/.gem/credential setting properly.

`gradlew gemPush` failed even $HOME/.gem/credential setting properly.

MRI gem worked properly even no setting changed.
(Ruby 3.2.2, gem 3.4.19)

I think It relates to JRuby issue.

### environment

* OS: macOS 13.5.2 (M1 mac)
* Java: Zulu 1.8.0_362

### log

```
ls -l /Users/user/.gem/credentials
-rw-------@ 1 user staff 81 Sep 14 13:40 /Users/user/.gem/credentials
```

```
./gradlew gemPush
Starting a Gradle Daemon (subsequent builds will be faster)
> Task :compileJava UP-TO-DATE
> Task :processResources NO-SOURCE
> Task :classes UP-TO-DATE
> Task :jar UP-TO-DATE
> Task :gem UP-TO-DATE

> Task :gemPush
Executing: `java org.jruby.Main -rjars/setup -S gem push /path/to/plugin/embulk-parser-jsonpath/build/gems/embulk-parser-jsonpath-0.4.1-java.gem --verbose`
with working directory at: /path/to/plugin/embulk-parser-jsonpath/build/gems
with classpath: [ /Users/user/.gradle/caches/modules-2/files-2.1/org.jruby/jruby-complete/9.2.7.0/308120bca38f617e7b275af8ce0cbd9f0be66218/jruby-complete-9.2.7.0.jar ]
ERROR: Your gem push credentials file located at:

/Users/user/.gem/credentials

has file permissions of 0644 but 0600 is required.

To fix this error run:

chmod 0600 /Users/user/.gem/credentials

You should reset your credentials at:

https://rubygems.org/profile/edit

if you believe they were disclosed to a third party.

> Task :gemPush FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':gemPush'.
> Process 'command '/Library/Java/JavaVirtualMachines/zulu-8.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 7.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/6.8.2/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 6s

4 actionable tasks: 1 executed, 3 up-to-date
```

[log2.txt](https://github.com/embulk/gradle-embulk-plugins/files/12614471/log2.txt)