oc-basic.el: Stringify year from CSL-JSON date-parts

* lisp/oc-basic.el (org-cite-basic--parse-json): Make sure year
extracted from date-parts is returned as string.  Raise error if
original type other than number or string.

The stringifiation is motivated by errors like the following on Emacs 28
with nativecomp:

Error during redisplay: (jit-lock-function 544) signaled
(wrong-type-argument "Argument is not a string or a secondary string:
2007")

Additionally, the type check will warn users about problems in their
CSL-JSON bibliographies.

Fixes https://list.orgmode.org/875ykv4k2q.fsf@localhost/T/#t

TINYCHANGE

lisp/oc-basic.el

@@ -189,7 +189,14 @@ Return a hash table with citation references as keys and fields alist as values.
                                 (cons 'year
                                       (cond
                                        ((consp date)
-                                        (caar date))
+                                         (let ((year (caar date)))
+                                           (cond
+                                             ((numberp year) (number-to-string year))
+                                             ((stringp year) year)
+                                             (t
+                                               (error
+                                                 "First element of CSL-JSON date-parts should be a number or string, got %s: %S"
+                                                 (type-of year) year)))))
                                        ((stringp date)
                                         (replace-regexp-in-string
                                           (rx