Replace bashism in src/bin/sage-env #30128
Description
The sage-env script is run under /bin/sh but contains bashisms:
SAGE_SCRIPTS_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
This causes a build failure when /bin/sh is not bash:
cd '/home/mjo/src/sage.git/build/pkgs/sage_conf' && . '/home/mjo/src/sage.git/src/bin/sage-env' && . '/home/mjo/src/sage.git/build/bin/sage-build-env-config' && sage-logger -p '/home/mjo/src/sage.git/build/pkgs/sage_conf/spkg-install' '/home/mjo/src/sage.git/logs/pkgs/sage_conf-none.log'
/bin/sh: 123: /home/mjo/src/sage.git/src/bin/sage-env: Bad substitution
Error: SAGE_SCRIPTS_DIR is set to a bad value:
SAGE_SCRIPTS_DIR=/home/mjo/src/sage.git/build/pkgs/sage_conf
You must correct it or erase it and rerun this script
make[3]: *** [Makefile:2022: /home/mjo/src/sage.git/local/var/lib/sage/installed/sage_conf-none] Error 1
The comment at the top of sage-env about using bash features should be removed afterwards. For bonus points, it would be nice if we could add a non-bash shell to one of the CI runs.
CC: @jhpalmieri
Component: build
Author: Michael Orlitzky
Branch/Commit: 554282a
Reviewer: Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/30128