refactor: reword RSC-004 message (encrypted files)

Fix #1235

src/main/resources/com/adobe/epubcheck/messages/MessageBundle.properties

@@ -254,7 +254,7 @@ PKG_027=Could not extract EPUB ZIP content, probably due to file names not encod
 RSC_001=File "%1$s" could not be found.
 RSC_002=Required META-INF/container.xml resource could not be found.
 RSC_003=No rootfile tag with media type "application/oebps-package+xml" was found in the container.
-RSC_004=File "%1$s" could not be decrypted.
+RSC_004=File "%1$s" is encrypted, its content will not be checked.
 RSC_005=Error while parsing file: %1$s
 RSC_006=Remote resource reference is not allowed in this context; resource "%1$s" must be located in the EPUB container.
 RSC_006b=Resource "%1$s" is located outside the EPUB Container; please check the resource is retrieved in scripted content.