gnu: flowee: Really disable black-box test.

* gnu/packages/finance.scm (flowee)[arguments]: The test 'api' has some
  timeouts which fail half the time in a build, so really disable the test.

Signed-off-by: Marius Bakke <marius@gnu.org>

gnu/packages/finance.scm

@@ -1546,6 +1546,8 @@ (define-public flowee
             (lambda _
               (substitute* "testing/CMakeLists.txt"
                 (("test_api") ""))
+              (substitute* "testing/CMakeLists.txt"
+                (("add_subdirectory\\(api\\)") ""))
               #t))
           (add-after 'configure 'set-build-info
             ;; Their genbuild.sh to generate a build.h fails in guix (no .git dir) .