IR text tests: Unmute tests that have main function

Don't use `main` function in these tests, because `main` function
has specific mangling rules in JVM. Use other function name.

^KT-57755

compiler/testData/ir/irText/firProblems/AssignmentOperator.kt.txt

@@ -36,7 +36,7 @@ fun <T : Any?> id(t: T): T {
   return t
 }
 
-fun main() {
+fun runMe() {
   val a: A = A()
   id<A>(t = a).<set-prop>(<set-?> = 10)
   { // BLOCK