infra(ci): raise test step timeout 10m → 15m for cold runner headroom (mc#1099)

golangci-lint --no-config --timeout 10m now passes on PR #1151, but the
go test -race -timeout 10m step hits its ceiling immediately after on
very-cold runners (~20m for lint + 10m for test = job fails at 30m).

Raising the test step timeout to 15m gives sufficient headroom for the
cold-cache race-enabled suite while staying well within the 50m job ceiling.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -198,10 +198,12 @@ jobs:
       - if: always()
         name: Run tests with race detection and coverage
         # Explicit timeout: cold runner cache causes OOM kills at ~4m39s on the
-        # full ./... suite with race detection + coverage. A 10m per-step timeout
-        # lets the suite complete on cold cache (~5-7m) while failing cleanly
+        # full ./... suite with race detection + coverage. A 15m per-step timeout
+        # lets the suite complete on cold cache (~5-12m) while failing cleanly
         # instead of OOM-killing. The job-level timeout (50m) is a backstop.
-        run: go test -race -timeout 10m -coverprofile=coverage.out ./...
+        # mc#1099: raised from 10m to 15m — cold runner test suite consistently
+        # hits 10m ceiling after golangci-lint ~20m on very-cold runner (PR #1151).
+        run: go test -race -timeout 15m -coverprofile=coverage.out ./...
 
       - if: always()
         name: Per-file coverage report