fix code typo in ExceptionFilter

[lewangdev]

What is the purpose of the change

Fix code typo

Brief changelog

Change exceptionClassses to exceptionClasses

Verifying this change

Verfied

[codecov-io]

Codecov Report

Merging #6932 (b6d5ba5) into master (3fc2d10) will decrease coverage by 0.09%.
The diff coverage is 50.00%.

@@             Coverage Diff              @@
##             master    #6932      +/-   ##
============================================
- Coverage     59.43%   59.33%   -0.10%     
+ Complexity      510      506       -4     
============================================
  Files          1028     1028              
  Lines         41519    41519              
  Branches       6037     6037              
============================================
- Hits          24678    24637      -41     
- Misses        14104    14132      +28     
- Partials       2737     2750      +13     

Impacted Files	Coverage Δ	Complexity Δ
...a/org/apache/dubbo/rpc/filter/ExceptionFilter.java	55.88% <50.00%> (ø)	0.00 <0.00> (ø)
...bo/config/event/listener/LoggingEventListener.java	37.50% <0.00%> (-25.00%)	0.00% <0.00%> (ø%)
...ava/org/apache/dubbo/config/DubboShutdownHook.java	63.82% <0.00%> (-10.64%)	0.00% <0.00%> (ø%)
...ng/transport/dispatcher/all/AllChannelHandler.java	82.75% <0.00%> (-6.90%)	0.00% <0.00%> (ø%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	55.68% <0.00%> (-4.55%)	20.00% <0.00%> (-1.00%)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0.00%> (-4.35%)	0.00% <0.00%> (ø%)
...pache/dubbo/remoting/transport/AbstractServer.java	53.75% <0.00%> (-3.75%)	0.00% <0.00%> (ø%)
...mmon/serialize/kryo/utils/AbstractKryoFactory.java	75.43% <0.00%> (-3.51%)	0.00% <0.00%> (ø%)
...he/dubbo/remoting/transport/netty/NettyServer.java	70.17% <0.00%> (-3.51%)	8.00% <0.00%> (-1.00%)
...g/apache/dubbo/rpc/protocol/rest/RestProtocol.java	68.21% <0.00%> (-3.11%)	0.00% <0.00%> (ø%)
... and 12 more

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