Fix a build failure on ruby 3.2.0dev (2022-10-20)

The expected error massage pattern was

```
in_buggy.rb:5: syntax error, unexpected end-of-input, expecting
```

but the actual error message on Ruby 3.2 is

```
in_buggy.rb:5: syntax error, unexpected end-of-input (SyntaxError)
```

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

test/command/test_fluentd.rb

@@ -523,7 +523,7 @@ def assert_fluentd_fails_to_start(cmdline, *pattern_list, timeout: 10)
 
       assert_fluentd_fails_to_start(
         create_cmdline(conf_path, "-p", File.dirname(plugin_path)),
-        "in_buggy.rb:5: syntax error, unexpected end-of-input, expecting"
+        "in_buggy.rb:5: syntax error, unexpected end-of-input"
       )
     end
   end