Fix idle resource removal in the resource pool

tests/resource-pool.scm

@@ -72,6 +72,27 @@
 
      (destroy-resource-pool resource-pool))))
 
+(run-fibers-for-tests
+ (lambda ()
+   (let ((resource-pool (make-resource-pool
+                         new-number
+                         2
+                         #:idle-seconds 0.5
+                         #:destructor
+                         (lambda (res)
+                           #t))))
+     (fibers-for-each
+      (lambda _
+        (with-resource-from-pool resource-pool
+            res
+          res))
+      (iota 20))
+
+     (let loop ((stats (resource-pool-stats resource-pool)))
+       (unless (= 0 (assq-ref stats 'resources))
+         (sleep 0.1)
+         (loop (resource-pool-stats resource-pool)))))))
+
 (run-fibers-for-tests
  (lambda ()
    (let* ((counter 0)