setup, requirements: bump to Python 3.9

sigstore >= 3.4 requires 3.9, so this action
does as well.

Signed-off-by: William Woodruff <[email protected]>

Author: woodruffw

requirements.txt

@@ -1,2 +1,2 @@
-sigstore ~= 3.0
+sigstore ~= 3.4
 requests ~= 2.28

setup/setup.bash

@@ -37,15 +37,15 @@ if [[ "${0}" == "${BASH_SOURCE[0]}" ]]; then
   die "Internal error: setup harness was executed instead of being sourced?"
 fi
 
-# Check the Python version, making sure it's new enough (3.8+)
+# Check the Python version, making sure it's new enough (3.9+)
 # The installation step immediately below will technically catch this,
 # but doing it explicitly gives us the opportunity to produce a better
 # error message.
 vers=$(python -V | cut -d ' ' -f2)
 maj_vers=$(cut -d '.' -f1 <<< "${vers}")
 min_vers=$(cut -d '.' -f2 <<< "${vers}")
 
-[[ "${maj_vers}" == "3" && "${min_vers}" -ge 8 ]] || die "Bad Python version: ${vers}"
+[[ "${maj_vers}" == "3" && "${min_vers}" -ge 9 ]] || die "Bad Python version: ${vers}"
 
 # If the user didn't explicitly configure a Python version with
 # `actions/setup-python`, then we might be using the distribution's Python and