[infra] Increase number of shards for debug precomp builder.

The tests were taking more than an hour on two of the shards, and timing out.

Change-Id: I1d242f827b50d2b9a3ddef705f8a54ee061bc101
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103120
Reviewed-by: Alexander Thomas <athom@google.com>
diff --git a/tools/bots/test_matrix.json b/tools/bots/test_matrix.json
index e39d0d6..4fcba4c 100644
--- a/tools/bots/test_matrix.json
+++ b/tools/bots/test_matrix.json
@@ -555,7 +555,6 @@
     },
     {
       "builders": [
-        "vm-kernel-precomp-linux-debug-x64",
         "vm-kernel-precomp-linux-product-x64",
         "vm-kernel-precomp-linux-release-simarm",
         "vm-kernel-precomp-linux-release-simarm64",
@@ -588,6 +587,32 @@
     },
     {
       "builders": [
+        "vm-kernel-precomp-linux-debug-x64"
+      ],
+      "meta": {
+        "description": "This configuration is used by the vm kernel precomp debug builders. It uses 15 shards for testing to avoid 1 hour shard timeouts."
+      },
+      "steps": [
+        {
+          "name": "build dart",
+          "script": "tools/build.py",
+          "arguments": [
+            "runtime_kernel",
+            "dart_precompiled_runtime"
+          ]
+        },
+        {
+          "name": "vm tests",
+          "arguments": [
+            "-ndartkp-${system}-${mode}-${arch}"
+          ],
+          "fileset": "vm-kernel",
+          "shards": 15
+        }
+      ]
+    },
+    {
+      "builders": [
         "vm-kernel-precomp-bare-linux-release-x64",
         "vm-kernel-precomp-bare-linux-release-simarm",
         "vm-kernel-precomp-bare-linux-release-simarm64"