tests: Move all PAM tests into a separate directory

As per
<https://github.com/NixOS/nixpkgs/pull/146467#issuecomment-972743535>.

nixos/tests/all-tests.nix

@@ -343,9 +343,9 @@ in
   osrm-backend = handleTest ./osrm-backend.nix {};
   overlayfs = handleTest ./overlayfs.nix {};
   packagekit = handleTest ./packagekit.nix {};
-  pam = handleTest ./pam/default.nix {};
-  pam-oath-login = handleTest ./pam-oath-login.nix {};
-  pam-u2f = handleTest ./pam-u2f.nix {};
+  pam-file-contents = handleTest ./pam/pam-file-contents.nix {};
+  pam-oath-login = handleTest ./pam/pam-oath-login.nix {};
+  pam-u2f = handleTest ./pam/pam-u2f.nix {};
   pantalaimon = handleTest ./matrix/pantalaimon.nix {};
   pantheon = handleTest ./pantheon.nix {};
   paperless-ng = handleTest ./paperless-ng.nix {};

nixos/tests/pam/pam-oath-login.nix

@@ -1,4 +1,4 @@
-import ./make-test-python.nix ({ ... }:
+import ../make-test-python.nix ({ ... }:
 
 let
   oathSnakeoilSecret = "cdd4083ef8ff1fa9178c6d46bfb1a3";

nixos/tests/pam/pam-u2f.nix

@@ -1,4 +1,4 @@
-import ./make-test-python.nix ({ ... }:
+import ../make-test-python.nix ({ ... }:
 
 {
   name = "pam-u2f";