Add test for connection error if certificate is not valid

Summary

caosdb-cpplib#97 (closed)

Test Environment

How to set up a test environment for manual testing?

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Makefile

@@ -67,7 +67,7 @@ build-debug: conan-install-debug
 
 build-release: conan-install-release
 	# cmake --preset conan-release # for CMake >= 3.23
-	@command -v iwyu || command include-what-you-use || \
+	@command -v iwyu || command -v include-what-you-use || \
 	  (echo "Could not find 'iwyu', exiting."; exit 1)
 	@command -v clang-tidy || command -v clang-tidy-16 || \
 	  (echo "Could not find 'clang-tidy'(-16), exiting."; exit 1)