It is using very long file names that can be too long if the workspace has a long name, it would appear. It looks like the file name could be half the size:
java.io.FileNotFoundException: longfilename-JDK_13-internal-0-2019-07-18-1830384.anthony.scarpino.stateless-update-CERT_nr3_DSA_SHA-512-DIGESTALG_SHA-512-signagainunmodified-JDK_13-internal-0-2019-07-18-1830384.anthony.scarpino.stateless-update-CERT_nr3_DSA_SHA-512-DIGESTALG_SHA-512.jar (File name too long)
at java.base/java.io.FileOutputStream.open0(Native Method)
at java.base/java.io.FileOutputStream.open(FileOutputStream.java:292)
at java.base/java.io.FileOutputStream.(FileOutputStream.java:235)
at java.base/java.io.FileOutputStream.(FileOutputStream.java:185)
at jdk.jartool/sun.security.tools.jarsigner.Main.signJar(Main.java:1633)
at jdk.jartool/sun.security.tools.jarsigner.Main.run(Main.java:269)
at jdk.jartool/sun.security.tools.jarsigner.Main.main(Main.java:118)