Fix checking out branch names with / chars

If git can't automatically figure out if the argument is a branch or
a path, it will need to be told explicitly by using `--`:

    Use '--' to separate paths from revisions, like this:
    'git <command> [<revision>...] -- [<file>...]'

Fixes: #106

entrypoint.sh

@@ -43,7 +43,7 @@ _switch_to_branch() {
     git fetch;
 
     # Switch to branch from current Workflow run
-    git checkout $INPUT_BRANCH;
+    git checkout "$INPUT_BRANCH" --;
 }
 
 _add_files() {