fix: avoid uisng 'pid' as log data field

[zmstone]

Since it clashes with log meta data field

Fixes https://emqx.atlassian.net/browse/EMQX-9315

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 4523719237

• 8 of 12 (66.67%) changed or added relevant lines in 3 files are covered.
• 36 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.04%) to 80.816%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/emqx_gateway/src/emqx_gateway_cm.erl	0	4	0.0%

Files with Coverage Reduction	New Missed Lines	%
apps/emqx_authn/src/enhanced_authn/emqx_enhanced_authn_scram_mnesia.erl	1	86.57%
apps/emqx_conf/src/emqx_cluster_rpc.erl	1	80.31%
apps/emqx_conf/src/emqx_conf_schema.erl	1	92.86%
apps/emqx_resource/src/emqx_resource_buffer_worker.erl	1	91.73%
apps/emqx_resource/src/emqx_resource_manager.erl	1	88.51%
apps/emqx_rule_engine/src/emqx_rule_engine.erl	1	85.83%
apps/emqx/src/emqx_channel.erl	1	87.64%
apps/emqx/src/emqx_vm.erl	1	83.65%
apps/emqx/src/emqx_crl_cache.erl	2	92.31%
apps/emqx_gateway/src/exproto/emqx_exproto_gcli.erl	3	48.78%

Totals
Change from base Build 4523620395:	-0.04%
Covered Lines:	24826
Relevant Lines:	30719

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💛 - Coveralls