Conformance: re-backslash-lower-z and upper-Z EXPR fixtures are byte-identical, so backslash-Z is never tested

[uberware]

Summary

In conformance-tests/2023-09/EXPR/job_templates/:

• expr2.2.5--re-backslash-lower-z.invalid.yaml and
  expr2.2.5--re-backslash-upper-Z.invalid.yaml are byte-for-byte identical
  (git blob 92d1159 for both on current main; md5 4e4ed82bbf9426c8580795ca03bcaebb).
• Both contain the pattern r"llo\z" — lowercase z — despite the "upper-Z" filename.
• Consequently nothing in the 2023-09 EXPR suite tests \Z at all, although RFC 0006
  excludes it from the dialect just as it excludes \z.

Suggested fix

Change the pattern in the upper-Z fixture to r"llo\Z" so the two fixtures test what
their names say, and \Z rejection gains coverage.