feat(global_defaults): validate user input against one argument spec on both paths

tests/users/users_fixtures.yml

@@ -52,7 +52,7 @@ users_fixtures:
         - name: ops
           password: pw
     expect:
-      fail: system.users must be a dict keyed by username
+      fail: "system.users: expected dict, got list"
 
   - name: list-rejected-precomputed
     precomputed: true
@@ -61,14 +61,14 @@ users_fixtures:
         - name: ops
           password: pw
     expect:
-      fail: system.users must be a dict keyed by username
+      fail: "system.users: expected dict, got list"
 
   - name: scalar-entry-rejected
     system:
       users:
         ops: pw
     expect:
-      fail: system.users.ops must be a dict
+      fail: "system.users.ops: expected dict, got str"
 
   - name: scalar-entry-rejected-precomputed
     precomputed: true
@@ -76,7 +76,7 @@ users_fixtures:
       users:
         ops: pw
     expect:
-      fail: system.users.ops must be a dict
+      fail: "system.users.ops: expected dict, got str"
 
   - name: keys-string-rejected
     system:
@@ -85,7 +85,7 @@ users_fixtures:
           password: pw
           keys: ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFixture ops
     expect:
-      fail: its keys a list of SSH public keys
+      fail: "system.users.ops.keys: expected list, got str"
 
   - name: no-password-rejected
     system: