fix some typos (#9771)

* fix some typos

Signed-off-by: cuishuang <imcusg@gmail.com>

* fix typo

Signed-off-by: cuishuang <imcusg@gmail.com>

csharp/src/Google.Protobuf/CodedInputStream.cs

diff --git a/csharp/src/Google.Protobuf/CodedInputStream.cs b/csharp/src/Google.Protobuf/CodedInputStream.cs
index 912c11f..96ae84c 100644
--- a/csharp/src/Google.Protobuf/CodedInputStream.cs
+++ b/csharp/src/Google.Protobuf/CodedInputStream.cs
@@ -431,7 +431,7 @@
         {
             // TODO(jtattermusch): if the message doesn't implement IBufferMessage (and thus does not provide the InternalMergeFrom method),
             // what we're doing here works fine, but could be more efficient.
-            // What happends is that we first initialize a ParseContext from the current coded input stream only to parse the length of the message, at which point
+            // What happens is that we first initialize a ParseContext from the current coded input stream only to parse the length of the message, at which point
             // we will need to switch back again to CodedInputStream-based parsing (which involves copying and storing the state) to be able to
             // invoke the legacy MergeFrom(CodedInputStream) method.
             // For now, this inefficiency is fine, considering this is only a backward-compatibility scenario (and regenerating the code fixes it).