Fix "actor still initializing when getHandler() called" with containers. #12557

Job	Run time
fixup / block-fixup	10s
labels / InternalPRRequired	3s
lint / bazel	3m 17s
test (linux, ubuntu-22.04) / bazel	9m 18s
test (macOS, macos-15) / bazel	11m 34s
test (linux-arm, ubuntu-22.04-arm) / bazel	8m 31s
test (linux-arm, ubuntu-22.04-arm, -debug) / bazel	8m 55s
test (windows, windows-2025) / bazel	31m 38s
test (linux, ubuntu-22.04, -asan) / bazel	3m 26s
Run workers-sdk tests	0s
labels / InternalPRRequired	3s
test (windows, windows-2025) / bazel	10m 40s
test (macOS, macos-15) / bazel	11m 34s
test (linux-arm, ubuntu-22.04-arm, -debug) / bazel	8m 55s
test (linux-arm, ubuntu-22.04-arm) / bazel	8m 31s
test (linux, ubuntu-22.04) / bazel	9m 18s
lint / bazel	3m 17s
fixup / block-fixup	10s
test (linux, ubuntu-22.04, -asan) / bazel	3m 26s
Run workers-sdk tests	5m 36s
	2h 18m 22s

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