Rev DevTools version to 2.8.0

This matches devtools tag v2.8.0: https://github.com/flutter/devtools/releases/tag/v2.8.0

Change-Id: I58ca4775539899f107e10daeef05a31566bb47cc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/218789
Reviewed-by: Ben Konyi <[email protected]>

Author: kenzieschmoll

DEPS

@@ -107,7 +107,7 @@ vars = {
   "dart_style_rev": "08b0294d0a500d5c02168ef57dcb8868d0c3cb48",
 
   "dartdoc_rev" : "520e64977de7a87b2fd5be56e5c2e1a58d55bdad",
-  "devtools_rev" : "8881a7caa9067471008a8e00750b161f53cdb843",
+  "devtools_rev" : "3a2f570813200e6dee141f3e7a9edcae5f31c2e8",
   "jsshell_tag": "version:88.0",
   "ffi_rev": "4dd32429880a57b64edaf54c9d5af8a9fa9a4ffb",
   "fixnum_rev": "16d3890c6dc82ca629659da1934e412292508bba",