nghttp3: enable static libraries

[Arusekk]

Testing the changes

• I tested the changes in this PR: briefly

Local build testing

• I built this PR locally for my native architecture, x86_64

[Duncaen]

Setting ENABLE_STATIC_LIB disables tests, which I don't think is a good idea.

https://github.com/ngtcp2/nghttp3/blob/e7a5a617ddf04b46eb7ce0ddaf3e318b1b46017d/CMakeOptions.txt#L10

[Arusekk]

Setting ENABLE_STATIC_LIB disables tests, which I don't think is a good idea.

https://github.com/ngtcp2/nghttp3/blob/e7a5a617ddf04b46eb7ce0ddaf3e318b1b46017d/CMakeOptions.txt#L10

cmake_dependent_option(BUILD_TESTING "Enable tests" ON "ENABLE_STATIC_LIB" OFF)

Actually it seems like it allows enabling tests:
https://cmake.org/cmake/help/latest/module/CMakeDependentOption.html#command:cmake_dependent_option

cmake_dependent_option(<variable> <help> <value> <condition> <else-value>)

[github-actions]

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[Arusekk]

Already done in 3c834d6. Thanks.