bash scripts not loading any of ~/.bash*

Context:

• M1 MacBook
• macOS Ventura 13.5.2
• zsh as default shell
• GNU coreutils installed by homebrew
• /opt/homebrew/opt/coreutils/libexec/gnubin added to path in ~/.bashrc, ~/.bash_profile, and ~/.bash_login

I have bash scripts that

• start with #!/usr/bin/env bash
• invoke date with parameters that work with GNU date (/opt/homebrew/opt/coreutils/libexec/gnubin) but not macOS date (/bin/date)
• fail when invoked interactively from zsh because the wrong date is invoked
  • this isn’t a guess, I checked with which date and echo $PATH and so on
  • it works if I run bash interactively first, and then invoke the script from bash rather than zsh

This looks like the path changes in ~/.bash* are not being loaded when zsh launches my scripts.

To confirm that, I added lines like echo ".bashrc" to each of ~/.bash*, and none of those messages appear when I run my scripts.

In zsh, which bash gives /opt/homebrew/bin/bash, and bash --version starts with GNU bash, version 5.2.15(1)-release (aarch64-apple-darwin22.1.0)

How do I get bash to load its configuration for scripts?