spack.yaml: Added valid compiler field

Author: CodeGat

spack.yaml

@@ -9,6 +9,7 @@ spack:
     access-om3-nuopc:
       require: '@git.0.3.0'
       variants: +install_libraries
+
     esmf:
       require: '@8.5.0'
       variants: +debug
@@ -29,7 +30,7 @@ spack:
       require: '@4.1.2'
 
     all:
-      compilers: [[email protected]]
+      compiler: [[email protected]]
   view: true
   concretizer:
     unify: true