cgns: make fortran dependency optional (spack#47867)

Author: alalazo

var/spack/repos/builtin/packages/cgns/package.py

@@ -38,8 +38,8 @@ class Cgns(CMakePackage):
     version("3.3.1", sha256="81093693b2e21a99c5640b82b267a495625b663d7b8125d5f1e9e7aaa1f8d469")
     version("3.3.0", sha256="8422c67994f8dc6a2f201523a14f6c7d7e16313bdd404c460c16079dbeafc662")
 
-    depends_on("c", type="build")  # generated
-    depends_on("fortran", type="build")  # generated
+    depends_on("c", type="build")
+    depends_on("fortran", type="build", when="+fortran")
 
     variant("hdf5", default=True, description="Enable HDF5 interface")
     variant("fortran", default=False, description="Enable Fortran interface")