[General][Java SDK (Component)] Add spi-extensions unit test

[heliang666s]

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Apache Dubbo Component

Java SPI Extensions (apache/dubbo-spi-extensions)

Details

At present, the codev of the Dubbo extension library shows that the test case coverage is very low, and the unit test case is optimized for this problem.Note: Due to the large number of modules in this project, you can only claim one module at a time, and then come back to claim the second one when you are done
Repository link: https://github.com/apache/dubbo-spi-extensions

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