[vm] Bump the oldest supported ABI version

Versions 3 and 4 aren't working:
https://logs.chromium.org/logs/dart/led/athom_google.com/00806a27a5b309ebe69e18cafd92b9aa9165e0eff8fcd3f41ec796e40b41f920/+/steps/run_tests/0/stdout

Change-Id: Id44e4e1bbd4719a9ae83eb76841eed7a4acece94
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/106560
Commit-Queue: Liam Appelbe <liama@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
diff --git a/tools/VERSION b/tools/VERSION
index 831acfe..5b4d144 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -36,4 +36,4 @@
 PRERELEASE 0
 PRERELEASE_PATCH 0
 ABI_VERSION 6
-OLDEST_SUPPORTED_ABI_VERSION 3
+OLDEST_SUPPORTED_ABI_VERSION 5