Fix date format

MatthewDaggitt · MatthewDaggitt · commit 90c16fffa671 · 2023-05-05T11:51:09.000+09:00
diff --git a/CITATION.cff b/CITATION.cff
@@ -4,5 +4,5 @@ authors:
 - name: "The Agda Community"
 title: "Agda Standard Library"
 version: 1.7.2
-date-released: 2023-2-1
+date-released: 2023-02-01
 url: "https://github.com/agda/agda-stdlib"
