fix: Document change detector breaking change (sourcenetwork#1531)

## Relevant issue(s)

Resolves sourcenetwork#1530 

## Description

This PR fixes the previous fix and adds a breaking change document to
prevent the broken cycle in the change detector after the fix. Should
have been part of the sourcenetwork#1528 although the change detector was passing
before merge.

docs/data_format_changes/i1530-change-detector-without-non-mutations.md

@@ -0,0 +1,3 @@
+# Change detector without non-mutations actions
+
+The previous fix caused a regression in the change detector and we need a documentation to break the cycle.

tests/integration/utils2.go

@@ -549,8 +549,6 @@ ActionLoop:
 		} else if firstNonSetupIndex > -1 {
 			// -1 to exclude this index
 			endIndex = firstNonSetupIndex - 1
-		} else {
-			startIndex = endIndex
 		}
 	} else {
 		if setupCompleteIndex > -1 {
@@ -560,6 +558,7 @@ ActionLoop:
 			// We must not set this to -1 :)
 			startIndex = firstNonSetupIndex
 		} else {
+			// if we don't have any non-mutation actions, just use the last action
 			startIndex = endIndex
 		}
 	}