NFC: Update Swift version to 5.7 in .swiftformat (#6290)

MaxDesiatov · web-flow · commit 57d829ac1bad · 2023-03-16T14:30:04.000-07:00
Since we have `swift-tools-version:5.7` in `Package.swift`, it makes sense to align `.swiftformat` with that version.
diff --git a/.swiftformat b/.swiftformat
@@ -1,6 +1,6 @@
 ## File options
 
---swiftversion 5.5
+--swiftversion 5.7
 --exclude .build
 
 ## Formatting options
