Fixed the issue where auto_observe was not working in LwM2M Gateway

[HJianBo]

Fixes https://emqx.atlassian.net/browse/EMQX-9362

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md and .zh.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• Change log has been added to changes/ dir for user-facing artifacts update

[coveralls]

Pull Request Test Coverage Report for Build 4542335129

• 9 of 9 (100.0%) changed or added relevant lines in 2 files are covered.
• 53 unchanged lines in 20 files lost coverage.
• Overall coverage decreased (-0.03%) to 80.946%

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Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authn/src/enhanced_authn/emqx_enhanced_authn_scram_mnesia.erl	1	86.57%
apps/emqx_bridge/src/emqx_bridge.erl	1	91.2%
apps/emqx_dashboard/src/emqx_dashboard_monitor.erl	1	65.28%
apps/emqx_gateway/src/mqttsn/emqx_sn_channel.erl	1	73.13%
apps/emqx_resource/src/emqx_resource_buffer_worker.erl	1	91.73%
apps/emqx_rule_engine/src/emqx_rule_engine.erl	1	85.83%
apps/emqx/src/emqx_cm.erl	1	91.44%
apps/emqx/src/emqx_limiter/src/emqx_limiter_schema.erl	1	90.91%
apps/emqx/src/emqx_router_helper.erl	1	86.27%
apps/emqx/src/emqx_session.erl	1	87.25%

Totals
Change from base Build 4541684260:	-0.03%
Covered Lines:	24975
Relevant Lines:	30854

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💛 - Coveralls