Fix "lines" and "functions" in coverage threshold guide (#12217)

docs/guides/test/coverage-threshold.md

@@ -52,7 +52,7 @@ Different thresholds can be set for line-level and function-level coverage.
 ```toml
 [test]
 # to set different thresholds for lines and functions
-coverageThreshold = { line = 0.5, function = 0.7 }
+coverageThreshold = { lines = 0.5, functions = 0.7 }
 ```
 
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