Update singularity version in DEF due to Node20 deprecation

Author: MihinP

.github/workflows/singularity.yml

@@ -12,7 +12,7 @@ jobs:
       fail-fast: false
       matrix:
         singularity_version:
-          - '3.8.1'
+          - '4.0'
 
     container:
       image: quay.io/singularity/singularity:v${{ matrix.singularity_version }}