Actually test bootstrap script of current branch

.github/workflows/bootstrap.sh

@@ -5,5 +5,4 @@ base=$(pwd)
 mkdir myproject
 cd myproject
 git init
-# Extract current bootstrap command from the docs.
-grep  "bootstrap | sh" $base/doc/source/user/install.txt | sed -e  's/\$//' | sh
+cat $base/bootstrap | sh