* lisp/oc.el (org-cite-adjust-note):
* lisp/oc-basic.el (org-cite-basic-goto):
* lisp/oc-biblatex.el (org-cite-biblatex-prepare-preamble):
* lisp/oc-csl.el (org-cite-csl--label-regexp): Avoid `rx' forms
introduced in Emacs-27.1 to keep compatibility with older versions.
Use `rx-to-string' instead of `rx' due to lack of support of `regexp'
and `literal' forms with a variable as an argument.
