secrets: fix sorting in `setup-secrets`

Now the bash globbing sort order equals the nix sort order
(order of `processedFiles`)
Previously, `comm` could fail with error `unsorted` on
specific secrets names.

modules/secrets/secrets.nix

@@ -173,6 +173,10 @@ in {
          RemainAfterExit = true;
       };
       script = ''
+        # Use the same sort order for globbing and sorting as in Nix attrsets.
+        # Required for `comm` below.
+        export LC_COLLATE=C
+
         ${optionalString cfg.generateSecrets ''
           mkdir -p "${cfg.secretsDir}"
           cd "${cfg.secretsDir}"