store: 'with-store' returns as many values as its body.

Fixes <https://bugs.gnu.org/42912>.
Reported by Ricardo Wurmus <rekado@elephly.net>.

* guix/store.scm (call-with-store)[thunk]: Wrap call to PROC in
'call-with-values'.
* tests/store.scm ("with-store, multiple values"): New test.

guix/store.scm

@@ -628,9 +628,10 @@ connection.  Use with care."
     (define (thunk)
       (parameterize ((current-store-protocol-version
                       (store-connection-version store)))
-        (let ((result (proc store)))
+        (call-with-values (lambda () (proc store))
+          (lambda results
             (close-connection store)
-          result)))
+            (apply values results)))))
 
     (cond-expand
       (guile-3

tests/store.scm

@@ -141,6 +141,15 @@
                     (string-append (%store-prefix) "/"
                                    (make-string 32 #\e) "-foobar"))))
 
+(test-equal "with-store, multiple values"        ;<https://bugs.gnu.org/42912>
+  '(1 2 3)
+  (call-with-values
+      (lambda ()
+        (with-store s
+          (add-text-to-store s "foo" "bar")
+          (values 1 2 3)))
+    list))
+
 (test-assert "valid-path? error"
   (with-store s
     (guard (c ((store-protocol-error? c) #t))