repos_manager: Reducing concurrency from 15 to 10

Summary:
reducing to 15 in D89545544 still wasn't enough, so let me try one last time reducing it to 10, to unblock a release bc the prod release is currently **very old**.

If this doesn't work, I'll wait for jagg to take a look when he's back on Monday.

Reviewed By: RajivTS

Differential Revision: D90020982

fbshipit-source-id: 7b71bee3394385b2c050aef135a371822cdb6bb3

Author: gustavoavena

eden/mononoke/cmdlib/mononoke_app/src/repos_manager.rs

@@ -219,8 +219,8 @@ impl<Repo> MononokeReposManager<Repo> {
                     anyhow::Ok((repo_id, repo_name, repo))
                 })
             })
-            // Repo construction can be heavy, 15 at a time is sufficient.
-            .buffer_unordered(15)
+            // Repo construction can be heavy, 10 at a time is sufficient.
+            .buffer_unordered(10)
             .map(|r| anyhow::Ok(r??))
             .try_collect::<Vec<_>>()
             .await?;
@@ -358,8 +358,8 @@ where
                     anyhow::Ok((repo_id, repo_name, repo))
                 })
             })
-            // Repo construction can be heavy, 15 at a time is sufficient.
-            .buffer_unordered(15)
+            // Repo construction can be heavy, 10 at a time is sufficient.
+            .buffer_unordered(10)
             .map(|r| anyhow::Ok(r??))
             .try_collect::<Vec<_>>()
             .await?;