Fix blocking call in FindByEmailAsync (#24116)

Author: HaoK

src/Identity/EntityFrameworkCore/src/UserStore.cs

@@ -322,7 +322,6 @@ protected override Task<TUserLogin> FindUserLoginAsync(string loginProvider, str
             return UserLogins.SingleOrDefaultAsync(userLogin => userLogin.LoginProvider == loginProvider && userLogin.ProviderKey == providerKey, cancellationToken);
         }
 
-
         /// <summary>
         /// Adds the given <paramref name="normalizedRoleName"/> to the specified <paramref name="user"/>.
         /// </summary>
@@ -637,7 +636,7 @@ public async override Task<TUser> FindByLoginAsync(string loginProvider, string
             cancellationToken.ThrowIfCancellationRequested();
             ThrowIfDisposed();
 
-            return Task.FromResult(Users.Where(u => u.NormalizedEmail == normalizedEmail).SingleOrDefault());
+            return Users.SingleOrDefaultAsync(u => u.NormalizedEmail == normalizedEmail);
         }
 
         /// <summary>
@@ -719,7 +718,6 @@ protected override Task AddUserTokenAsync(TUserToken token)
             return Task.CompletedTask;
         }
 
-
         /// <summary>
         /// Remove a new user token.
         /// </summary>