docs: add changelog entry

changes/ce/fix-12657.en.md

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+The rule engine SQL-based language previously did not allow putting any expressions as array elements in array literals (only constants and variable references where allowed). This has not been fixed so that one can use any expressions as array elements.
+
+The following is now permitted, for example:
+
+```
+select
+  [21 + 21, abs(-abs(-2)), [1 + 1], 4] as my_array
+from "t/#"
+```