Exclude */.git/* files when finding packages.apt

If a git branch name contains packages.apt, it can
break our jenkins script (see gazebosim/sdformat#392).

Signed-off-by: Steve Peters <scpeters@openrobotics.org>

jenkins-scripts/docker/lib/docker_generate_dockerfile.bash

@@ -267,7 +267,7 @@ DELIM_DOCKER_WORKAROUND_SIMBODY
 fi
 
 # Install debian dependencies defined on the source code
-SOURCE_DEFINED_DEPS="$(sort -u $(find . -iname 'packages-'$DISTRO'.apt' -o -iname 'packages.apt') | tr '\n' ' ')"
+SOURCE_DEFINED_DEPS="$(sort -u $(find . -iname 'packages-'$DISTRO'.apt' -o -iname 'packages.apt' | grep -v '/\.git/') | tr '\n' ' ')"
 
 # Packages that will be installed and cached by docker. In a non-cache
 # run below, the docker script will check for the latest updates