[io/win] Allow notFound stat errors in testDriveLetterNoBackslash.

Since the test uses existing system temp directory entries that
aren't created/maintained by the test itself, they may be removed
between the two calls to statSync().  Modify the test to allow for cases
where the first statSync() returns a non-notFound result and the second
returns a notFound result.

Also check that at least one iteration of the loop had a successful
result where the statSync() result is the same for both and was not a
notFound result, as all system temp entries retrieved by listSync()
being removed before one or both statSync() calls is highly unlikely.

TEST=standalone/io/file_windows_test

Fixes: #61007
Cq-Include-Trybots: luci.dart.try:vm-win-release-x64-try
Change-Id: If4bb4a6f6b1e21558e447e4e5a918523c69ff044
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/437442
Commit-Queue: Tess Strickland <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: sstrickl

tests/standalone/io/file_windows_test.dart

@@ -26,6 +26,7 @@ void testDriveLetterStat() {
 // converted refer to the same thing.
 void testDriveLetterNoBackslash() {
   final current = Directory.current.path;
+  var allFailed = true;
   for (var e in Directory.systemTemp.listSync()) {
     final path = e.path;
     if (path.length < 3) return;
@@ -40,12 +41,22 @@ void testDriveLetterNoBackslash() {
         }
       }
       noBackslash += path.substring(3);
-      Expect.equals(
-        "${Directory(noBackslash).statSync()}",
-        "${Directory(path).statSync()}",
-      );
+      final noBackslashStat = Directory(noBackslash).statSync();
+      final pathStat = Directory(path).statSync();
+      if (noBackslashStat.type != pathStat.type) {
+        // Since these are entries in the system temp directory, they may
+        // be removed between the two calls.
+        Expect.notEquals(FileSystemEntityType.notFound, noBackslashStat.type);
+        Expect.equals(FileSystemEntityType.notFound, pathStat.type);
+      } else {
+        Expect.stringEquals(noBackslashStat.toString(), pathStat.toString());
+        if (noBackslashStat.type != FileSystemEntityType.notFound) {
+          allFailed = false;
+        }
+      }
     }
   }
+  Expect.isFalse(allFailed, "no successful statSync() comparisons");
 }
 
 void testDeleteLongPathPrefix() {