[infra] Adjust build windows-arm64 split to avoid timeouts.

Fixes https://ci.chromium.org/ui/p/dart/builders/ci.sandbox/pkg-win-release-arm64/3781.

With new split the steps are distributed roughly like this:
```
$ RBE=0 tools/build.py -mrelease -ax64  gen_snapshot
[982/982] LINK ./gen_snapshot
The build took 39.285 seconds
$ RBE=0 tools/build.py -mrelease -ax64 runtime/bin:dart runtime/bin:run_vm_tests
[1392/1392] LINK ./run_vm_tests
The build took 97.936 seconds
$ RBE=0 tools/build.py -mrelease -ax64 runtime
[1223/1223] ACTION //utils/kernel-service:frontend_server_aot_product(//build/toolchain/linux:clang_x64)
The build took 97.168 seconds
$ RBE=0 tools/build.py -mrelease -ax64 create_sdk ddc_stable_test
[402/402] COPY gen/dart2js_aot_product.dart.snapshot dart-sdk/bin/snapshots/dart2js_aot.dart.snapshot
The build took 100.373 seconds
```

Also add Ryan to the OWNERS_INFRA.

Change-Id: Ibbf1a13ccd33d7bcb366ac864b05e960e5d73b8b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404201
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>

tools/OWNERS_INFRA

@@ -1 +1,2 @@
 athom@google.com
+rmacnak@google.com

tools/bots/test_matrix.json

@@ -3203,14 +3203,29 @@
           ]
         },
         {
-          "name": "build dart - step 1 - divided to avoid timeout",
+          "name": "build dart - step 1 - gen-snapshot - divided to avoid timeout",
+          "script": "tools/build.py",
+          "arguments": [
+            "gen_snapshot"
+          ]
+        },
+        {
+          "name": "build dart - step 2 - runtime/bin:dart - divided to avoid timeout",
+          "script": "tools/build.py",
+          "arguments": [
+            "runtime/bin:dart",
+            "runtime/bin:run_vm_tests"
+          ]
+        },
+        {
+          "name": "build dart - step 3 - runtime - divided to avoid timeout",
           "script": "tools/build.py",
           "arguments": [
             "runtime"
           ]
         },
         {
-          "name": "build dart - step 2 - divided to avoid timeout",
+          "name": "build dart - step 4 - sdk, ddc_stable_test - divided to avoid timeout",
           "script": "tools/build.py",
           "arguments": [
             "create_sdk",