Bump to v2.3.0rc1 without tbump

[forsyth2]

Bump to 2.3.0rc1.

Had to do this PR manually rather than using tbump. With tbump, I kept running into the following error:

[v2.3.0rc1 b66f311] Bump to 2.3.0rc1
 4 files changed, 4 insertions(+), 4 deletions(-)
To github.com:E3SM-Project/zppy.git
 ! [rejected]        main -> main (non-fast-forward)
error: failed to push some refs to 'github.com:E3SM-Project/zppy.git'
hint: Updates were rejected because a pushed branch tip is behind its remote
hint: counterpart. Check out this branch and integrate the remote changes
hint: (e.g. 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
Error: Command `git push upstream main` failed