[FIR][tests] Unify IntArrayAsVararg.kt test between K1 and K2

Rename `main` function to `test` to avoid running JVM-specific mangling
and having different IR signature dumps for K1 and K2.

^KT-65588

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

@@ -1,4 +1,4 @@
-fun main() {
+fun test() {
   consumeVarargs(arr = [1, 2])
   consumeVarargs(arr = [*intArrayOf(elements = [41, 42])])
 }