Add note about Monitor thread affinity (dotnet#9008)

The [remarks section](https://learn.microsoft.com/en-us/dotnet/api/system.threading.monitor?view=net-7.0#remarks) of the Monitor class does not mention the fact that the Monitor class has thread affinity.

That important information is found in a [separate article on synchronization primitives](https://learn.microsoft.com/en-us/dotnet/standard/threading/overview-of-synchronization-primitives#monitor-class) that is easy to miss.

I copied the relevant sentence and just tacked it onto the end of the paragraph in the Remarks section (it can be moved anywhere in the article, I just feel it's important to have it appear early on in the Remarks section because that's where I came looking for it).

Author: ericmutta

xml/System.Threading/Monitor.xml

@@ -56,7 +56,7 @@
       <format type="text/markdown"><![CDATA[  
   
 ## Remarks  
- The <xref:System.Threading.Monitor> class allows you to synchronize access to a region of code by taking and releasing a lock on a particular object by calling the <xref:System.Threading.Monitor.Enter%2A?displayProperty=nameWithType>, <xref:System.Threading.Monitor.TryEnter%2A?displayProperty=nameWithType>, and <xref:System.Threading.Monitor.Exit%2A?displayProperty=nameWithType> methods. Object locks provide the ability to restrict access to a block of code, commonly called a critical section. While a thread owns the lock for an object, no other thread can acquire that lock. You can also use the <xref:System.Threading.Monitor> class to ensure that no other thread is allowed to access a section of application code being executed by the lock owner, unless the other thread is executing the code using a different locked object.  
+ The <xref:System.Threading.Monitor> class allows you to synchronize access to a region of code by taking and releasing a lock on a particular object by calling the <xref:System.Threading.Monitor.Enter%2A?displayProperty=nameWithType>, <xref:System.Threading.Monitor.TryEnter%2A?displayProperty=nameWithType>, and <xref:System.Threading.Monitor.Exit%2A?displayProperty=nameWithType> methods. Object locks provide the ability to restrict access to a block of code, commonly called a critical section. While a thread owns the lock for an object, no other thread can acquire that lock. You can also use the <xref:System.Threading.Monitor> class to ensure that no other thread is allowed to access a section of application code being executed by the lock owner, unless the other thread is executing the code using a different locked object. Because the Monitor class has thread affinity, the thread that acquired a lock must release the lock by calling the Monitor.Exit method. 
   
  In this article: