tests: internal: signv4: skip Signv4 unit testing on Windows (#1856)
tests: internal: signv4: skip Signv4 unit testing on Windows (#1856)

This should fix the build failure on AppVeyor.

The test program for Signv4 depends on `dirent.h` for test suite
discovery. However, since Windows provides neither `dirent.h` nor
its equivalent functions, we cannot easily port the testing script
to Windows.

So this disables the signv4 testing for now. We need to revisit
this issue after we prepare a compatiblity layer for dirent.h.

Signed-off-by: Fujimoto Seiji <ef879192bb1e41d519c82cf76440dc8e9a530806@clear-code.com>
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