Raise .NET SDK test job timeout for slow macOS shard

After rebasing onto the newer runtime/dependency baseline, the macOS default
CAPI shard 1 was canceled while still running tests. All other .NET shards
passed, so keep the diagnostic job bound but raise it from 20 to 30 minutes to
avoid canceling a slow-but-healthy shard without logs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SteveSandersonMS

.github/workflows/dotnet-sdk-tests.yml

@@ -201,8 +201,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     # A hung test used to run until the runner died (~50 min) and the dying
     # runner never uploaded its logs, so the failures were undiagnosable.
-    # Every healthy cell finishes well under 15 min.
-    timeout-minutes: 20
+    # Most healthy cells finish well under 15 min, but macOS shard 1 can run
+    # longer on the smallest runner after runtime/dependency updates. Keep the
+    # job bound high enough that slow-but-healthy shards aren't canceled without
+    # diagnostics.
+    timeout-minutes: 30
     defaults:
       run:
         shell: bash