[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

@@ -2,10 +2,7 @@
 // WITH_STDLIB
 // ISSUE: KT-60312
 
-// SEPARATE_SIGNATURE_DUMP_FOR_K2
-// ^ The main function has a different mangled name when it's computed from its K1 descriptor in K/JVM.
-
-fun main() {
+fun test() {
     consumeVarargs(1, 2)
     consumeVarargs(arr = intArrayOf(41, 42))
 }