[Bug] Fix gradle build on Windows failing from a recent change (#765)

A recent change as part of the commit c2e816ec introduced a bug where the build is failing on Windows. The change was made to include the NOTICE.txt file as read-only in the distributions. The code fails on Windows as it's not a POSIX-compliant. This commit adds a check on the current operating system.

Signed-off-by: Rabi Panda <adnapibar@gmail.com>

buildSrc/src/main/groovy/org/opensearch/gradle/NoticeTask.groovy

@@ -152,8 +152,10 @@ class NoticeTask extends DefaultTask {
             }
         }
         outputFile.setText(output.toString(), 'UTF-8')
+        if (OS.current() != OS.WINDOWS) {
             Files.setPosixFilePermissions(outputFile.toPath(), PosixFilePermissions.fromString("rw-r--r--"))
         }
+    }
 
     @InputFiles
     @Optional