use exists() instead of count()

we only need to check for existence of a record here, not for the actual count, and `exists()` is generally more performant than a count.

src/Illuminate/Testing/Constraints/HasInDatabase.php

@@ -51,7 +51,9 @@ public function __construct(Connection $database, array $data)
      */
     public function matches($table): bool
     {
-        return $this->database->table($table)->where($this->data)->count() > 0;
+        return $this->database->table($table)
+            ->where($this->data)
+            ->exists();
     }
 
     /**

src/Illuminate/Testing/Constraints/NotSoftDeletedInDatabase.php

@@ -61,7 +61,7 @@ public function matches($table): bool
         return $this->database->table($table)
                 ->where($this->data)
                 ->whereNull($this->deletedAtColumn)
-                ->count() > 0;
+                ->exists();
     }
 
     /**

src/Illuminate/Testing/Constraints/SoftDeletedInDatabase.php

@@ -63,7 +63,7 @@ public function matches($table): bool
         return $this->database->table($table)
                 ->where($this->data)
                 ->whereNotNull($this->deletedAtColumn)
-                ->count() > 0;
+                ->exists();
     }
 
     /**