util/sem: remove tidb_slow_txn_log_threshold from invisible variable list (#64634)

close pingcap/tidb#64633

AGENTS.md

@@ -111,4 +111,4 @@ The PR title **must** strictly adhere to the following format. It uses the packa
 
 ### PR description
 
-The PR description **must** strictly follow the template located at @.github/pull_request_template.md and **must** keep HTML comment elements in the pull request description according to the pull request template. These elements are essential for CI and removing them will cause processing failures.
+The PR description **must** strictly follow the template located at @.github/pull_request_template.md and **must** keep the HTML comment elements like `Tests <!-- At least one of them must be included. -->` unchanged in the pull request description according to the pull request template. These elements are essential for CI and removing them will cause processing failures.

pkg/util/sem/compat/testhelper.go

@@ -121,7 +121,6 @@ var compatibleSEMV2Config = `{
 		{"name": "tidb_row_format_version", "hidden": true},
 		{"name": "tidb_slow_query_file", "hidden": true},
 		{"name": "tidb_slow_log_threshold", "hidden": true},
-		{"name": "tidb_slow_txn_log_threshold", "hidden": true},
 		{"name": "tidb_enable_collect_execution_info", "hidden": true},
 		{"name": "tidb_memory_usage_alarm_ratio", "hidden": true},
 		{"name": "tidb_redact_log", "hidden": true},

pkg/util/sem/sem.go

@@ -150,7 +150,6 @@ func IsInvisibleSysVar(varNameInLower string) bool {
 		vardef.TiDBRowFormatVersion,
 		vardef.TiDBSlowQueryFile,
 		vardef.TiDBSlowLogThreshold,
-		vardef.TiDBSlowTxnLogThreshold,
 		vardef.TiDBEnableCollectExecutionInfo,
 		vardef.TiDBMemoryUsageAlarmRatio,
 		vardef.TiDBRedactLog,