[infra] Fix typo in test matrix (#32229)

This fixes the problem that the dartkp-obfuscate builder was running the
wrong tests.

TBR=whesse@google.com

Change-Id: I7b2d2ca309a9b460f14a392414f6f594834b6a05
Reviewed-on: https://dart-review.googlesource.com/74140
Reviewed-by: Alexander Thomas <athom@google.com>

Author: athomas

tools/bots/test_matrix.json

@@ -364,7 +364,7 @@
         "use-blobs": true
     }},
     "dartkp-linux-(product|release)-x64": { },
-    "dartkp-obsufcate-linux-release-x64": {
+    "dartkp-obfuscate-linux-release-x64": {
       "options": {
         "builder-tag": "obfuscated",
         "vm-options": ["--obfuscate"]