Fix mise activate failing with unbound variable error
What
Fix mise activate failing with unbound variable error
Why
When running with 'set -u', mise activate bash fails because it sets PROMPT_COMMAND which triggers an unbound variable error in bash 4+.
Temporarily disable unbound variable checking around mise activation, and also quiet the plugin update output.
Fixes: bash: line 9: PROMPT_COMMAND: unbound variable
Note that this is failing only on bash 4+. Because we do #!/usr/bin/env bash instead of hard-coding #/bin/bash, it uses my homebrew-provided bash 5, which is stricter about unbound variables.
I'd rather increase compatibility than forcing an older bash version via hardcoded path.