Change custom script examples file extensions:

fixes shadowing of the gradle script definitions after these example
script defs are loaded via discovery mechanisms

libraries/examples/scripting/jvm-simple-script/host/test/org/jetbrains/kotlin/script/examples/jvm/simple/test/simpleTest.kt

@@ -15,7 +15,7 @@ class SimpleTest {
 
     @Test
     fun testSimple() {
-        val res = evalFile(File("testData/hello.kts"))
+        val res = evalFile(File("testData/hello.simplescript.kts"))
 
         Assert.assertTrue(
             "test failed:\n  ${res.reports.joinToString("\n  ") { it.message + if (it.exception == null) "" else ": ${it.exception}" }}",
@@ -25,7 +25,7 @@ class SimpleTest {
 
     @Test
     fun testError() {
-        val res = evalFile(File("testData/error.kts"))
+        val res = evalFile(File("testData/error.simplescript.kts"))
 
         Assert.assertTrue(
             "test failed - expecting a failure with the message \"Unresolved reference: abracadabra\" but received " +