tests: fix slack notification and make the login more readable (#2896)
tests: fix slack notification and make the login more readable (#2896)


cpanato/tectonic-installer,hhoover/tectonic-installer,kyoto/tectonic-installer,hhoover/tectonic-installer,kalmog/tectonic-installer,squat/tectonic-installer,derekhiggins/installer,kyoto/tectonic-installer,cpanato/tectonic-installer,cpanato/tectonic-installer,kyoto/tectonic-installer,kyoto/tectonic-installer,lander2k2/tectonic-installer,kalmog/tectonic-installer,hhoover/tectonic-installer,lander2k2/tectonic-installer,hhoover/tectonic-installer,squat/tectonic-installer,lander2k2/tectonic-installer,cpanato/tectonic-installer,derekhiggins/installer,lander2k2/tectonic-installer,kyoto/tectonic-installer,hhoover/tectonic-installer,squat/tectonic-installer,kalmog/tectonic-installer,squat/tectonic-installer