Move the CI "name" and "email" to constants for future reuse

Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>

package-source-builder/overlay/usr/bin/apertis-pkg-merge-updates

@@ -24,6 +24,9 @@ from pathlib import Path
 from debian.debian_support import Version
 from debian.changelog import Changelog
 
+APERTIS_CI_NAME = 'Apertis CI'
+APERTIS_CI_EMAIL = 'devel@lists.apertis.org'
+
 def git_dir() -> str:
     return git('rev-parse', '--git-dir').strip('\n')
 
@@ -49,7 +52,7 @@ def configure_git_user(name, email):
 
 def prepare_git_repo(upstream_branch):
   run(['git', 'branch', '-f', upstream_branch, 'origin/' + upstream_branch])
-  configure_git_user('Apertis CI', 'devel@lists.apertis.org')
+  configure_git_user(APERTIS_CI_NAME, APERTIS_CI_EMAIL)
   configure_git_merge()
 
 def get_package_name():