Raise the timer of names performance

Commit 929b758 introduced a decrease of
20 seconds -- from 30 seconds to 10 seconds -- because it was being
optimistic.

This timer is the responsible of making this test pass, and though 10
seconds is a very good time and we've passed it, it can happen that
compilation lasts more than expected and fails the tests.

For that reason, and to find a good tradeoff, this commit raises the
timer from 10 seconds to 20 seconds, 1/3 less of what we had originally
before this PR.

internal/compiler-bridge/src/test/scala/xsbt/ExtractUsedNamesPerformanceSpecification.scala

@@ -37,7 +37,7 @@ class ExtractUsedNamesPerformanceSpecification extends UnitSpec {
       zipfs.foreach { fs => try fs.close catch { case _: Throwable => /*ignore*/ } }
     import org.scalatest.concurrent.Timeouts._
     import org.scalatest.time.SpanSugar._
-    val usedNames = failAfter(10 seconds) {
+    val usedNames = failAfter(20 seconds) {
       val compilerForTesting = new ScalaCompilerForUnitTesting(nameHashing = true)
       compilerForTesting.extractUsedNamesFromSrc(src)
     }