[Test] Speculatively fix a non-deterministic issue

Somehow, `deinit` isn't called deterministically. Instead of using
`deinit` to print out the summary, use `finalize()` which is intended to
be finalize the diagnostics.

Fixes rdar://problem/71046813

Author: rintaro

Sources/lit-test-helper/main.swift

@@ -424,7 +424,6 @@ func printParserDiags(args: CommandLineArguments) throws {
   class ParserDiagPrinter: DiagnosticConsumer {
     var counter : (error: Int, warning: Int, note: Int) = (0, 0, 0)
     var calculateLineColumn: Bool { return true }
-    func finalize() {}
     func handle(_ diag: Diagnostic) {
       switch diag.message.severity {
       case .error:
@@ -438,7 +437,7 @@ func printParserDiags(args: CommandLineArguments) throws {
       }
       print(diag.debugDescription)
     }
-    deinit {
+    func finalize() {
       print("\(counter.error) error(s) \(counter.warning) warnings(s) \(counter.note) note(s)")
     }
   }