Relax ordering constraints in oximeter counter tests (#7262)

- Allow server and collection-task-side counters to differ by at most
one in tests checking that we track requests in the task.
- Fixes #7255

oximeter/collector/src/agent.rs

@@ -745,9 +745,9 @@ mod tests {
         let count = stats.collections.datum.value() as usize;
 
         assert!(count != 0);
-        assert_eq!(
-            count,
-            collection_count.load(Ordering::SeqCst),
+        let server_count = collection_count.load(Ordering::SeqCst);
+        assert!(
+            count == server_count || count - 1 == server_count,
             "number of collections reported by the collection \
             task differs from the number reported by the empty \
             producer server itself"
@@ -892,9 +892,16 @@ mod tests {
 
         assert_eq!(stats.collections.datum.value(), 0);
         assert!(count != 0);
-        assert_eq!(
-            count,
-            collection_count.load(Ordering::SeqCst),
+
+        // The server may have handled a request that we've not yet recorded on
+        // our collection task side, so we allow the server count to be greater
+        // than our own. But since the collection task is single-threaded, it
+        // cannot ever be more than _one_ greater than our count, since we
+        // should increment that counter before making another request to the
+        // server.
+        let server_count = collection_count.load(Ordering::SeqCst);
+        assert!(
+            count == server_count || count - 1 == server_count,
             "number of collections reported by the collection \
             task differs from the number reported by the always-ded \
             producer server itself"