[type: refactor]Replace with computeIfAbsent.

[KevinClair]

Make sure that:

• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[codecov-commenter]

Codecov Report

Merging #4017 (79ecc7c) into master (bf2f474) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #4017      +/-   ##
============================================
- Coverage     70.12%   70.02%   -0.11%     
+ Complexity     6713     6706       -7     
============================================
  Files           927      927              
  Lines         25294    25291       -3     
  Branches       2283     2282       -1     
============================================
- Hits          17738    17710      -28     
- Misses         6167     6192      +25     
  Partials       1389     1389              

Impacted Files	Coverage Δ
...henyu/loadbalancer/spi/RoundRobinLoadBalancer.java	92.00% <100.00%> (-0.46%)	⬇️
...henyu/plugin/grpc/resolver/ShenyuNameResolver.java	58.51% <0.00%> (-13.83%)	⬇️
...henyu/common/cache/MemorySafeWindowTinyLFUMap.java	72.41% <0.00%> (-8.63%)	⬇️
.../plugin/grpc/loadbalance/AbstractLoadBalancer.java	70.65% <0.00%> (-7.61%)	⬇️
...n/alibaba/dubbo/cache/AlibabaDubboConfigCache.java	77.01% <0.00%> (-1.15%)	⬇️
...gin/apache/dubbo/cache/ApacheDubboConfigCache.java	74.15% <0.00%> (-1.13%)	⬇️
...henyu/admin/service/impl/UpstreamCheckService.java	64.00% <0.00%> (+1.33%)	⬆️

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