FIR CFG: merge data flow if called-in-place lambda may not be called

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/plusAssignWithLambdaInRhs.dot

@@ -146,8 +146,7 @@ digraph plusAssignWithLambdaInRhs_kt {
     37 -> {38};
     38 -> {39};
     39 -> {40};
-    40 -> {45};
-    40 -> {41} [color=red];
+    40 -> {41 45};
     40 -> {45} [style=dashed];
     41 -> {42};
     42 -> {43};
@@ -157,7 +156,7 @@ digraph plusAssignWithLambdaInRhs_kt {
     47 -> {48};
     48 -> {49};
     49 -> {50};
-    50 -> {41} [color=green];
+    50 -> {41};
     50 -> {45} [color=green style=dashed];
 
 }