Change 'data' to 'sequence' in for loop documentation example

Co-authored-by: felix-andreas <[email protected]>

Author: Copilot

crates/roughly/tests/snapshots/test_format__documentation_examples__for_loops.snap

@@ -2,6 +2,6 @@
 source: crates/roughly/tests/test_format.rs
 expression: code
 ---
-for (item in data) {
+for (item in sequence) {
   process(item)
 }