Improve organization of CI workflow scripts and pip requirements (#45037)

.github/workflows/bin/setup_git.sh

@@ -0,0 +1,8 @@
+#!/bin/bash -e
+git config --global user.email "spack@example.com"
+git config --global user.name "Test User"
+
+# create a local pr base branch
+if [[ -n $GITHUB_BASE_REF ]]; then
+    git fetch origin "${GITHUB_BASE_REF}:${GITHUB_BASE_REF}"
+fi