CI: add executable script .github/setup.sh

Author: tpietzsch

.github/setup.sh

@@ -1,3 +1,3 @@
 #!/bin/sh
-curl -fsLO https://raw.githubusercontent.com/scijava/scijava-scripts/master/ci-setup-github-actions.sh
+curl -fsLO https://raw.githubusercontent.com/scijava/scijava-scripts/main/ci-setup-github-actions.sh
 sh ci-setup-github-actions.sh