Fix a typo (#9652)

* Fix a typo

Just a minor typo.

Author: b4ry

xml/System.Threading/ReaderWriterLockSlim.xml

@@ -487,7 +487,7 @@
 ## Examples
  The following example shows how to use the <xref:System.Threading.ReaderWriterLockSlim.EnterUpgradeableReadLock%2A> method to enter the lock in upgradeable mode. A `finally` block is used to execute the <xref:System.Threading.ReaderWriterLockSlim.ExitUpgradeableReadLock%2A> method, ensuring that the caller exits upgradeable mode.
 
- The method shown in the example retrieves the value associated with a key and compares it with a new value. If the value is unchanged, the method returns a status indicating no change. It no value is found for the key, the key/value pair is inserted. If the value has changed, it is updated. Upgradeable mode allows the thread to upgrade the read lock as needed, without risk of deadlocks.
+ The method shown in the example retrieves the value associated with a key and compares it with a new value. If the value is unchanged, the method returns a status indicating no change. If no value is found for the key, the key/value pair is inserted. If the value has changed, it is updated. Upgradeable mode allows the thread to upgrade the read lock as needed, without risk of deadlocks.
 
  The example uses the parameterless constructor to create the lock, so recursion is not allowed. Programming the <xref:System.Threading.ReaderWriterLockSlim> is simpler and less prone to error when the lock does not allow recursion.
 
@@ -703,7 +703,7 @@
 ## Examples
  The following example shows how to use a `finally` block to execute the <xref:System.Threading.ReaderWriterLockSlim.ExitUpgradeableReadLock%2A> method, ensuring that the caller exits upgradeable mode.
 
- The method shown in the example retrieves the value associated with a key and compares it with a new value. If the value is unchanged, the method returns a status indicating no change. It no value is found for the key, the key/value pair is inserted. If the value has changed, it is updated. Upgradeable mode allows the thread to upgrade the read lock as needed, without risk of deadlocks.
+ The method shown in the example retrieves the value associated with a key and compares it with a new value. If the value is unchanged, the method returns a status indicating no change. If no value is found for the key, the key/value pair is inserted. If the value has changed, it is updated. Upgradeable mode allows the thread to upgrade the read lock as needed, without risk of deadlocks.
 
  The example uses the parameterless constructor to create the lock, so recursion is not allowed. Programming the <xref:System.Threading.ReaderWriterLockSlim> is simpler and less prone to error when the lock does not allow recursion.