Inverted condition to ensure if statement is correct

Author: droberts-ctrlo

.github/workflows/install.sh

@@ -23,7 +23,7 @@ apt-get install -y libstring-camelcase-perl libtest-mocktime-perl libtest-most-p
 apt-get install -y libtext-csv-encoded-perl libtext-markdown-perl libtie-cache-perl libtree-dagnode-perl liburl-encode-perl
 apt-get install -y libwww-form-urlencoded-xs-perl libwww-mechanize-chrome-perl libwww-mechanize-perl libyaml-perl postfix
 apt-get install -y postgresql-client starman perl libtest-tempdir-tiny-perl
-if [[ -z "GADS_USERNAME" ]]
+if [[ !(-z "GADS_USERNAME") ]]
 then
     apt install -y unzip gconf2 libgtk2.0-0 libgtk-3-0 libgbm-dev libnotify-dev libnss3 libxss1 libasound2 libxtst6 xauth xvfb
     cpanm --notest WebDriver::Tiny