[promtail] Chore(prometheus-rule):

[yaskinny]

In the chart's default values file, there are two rules which people might use them. In case something goes wrong at network level like TCP connection timeout, Promtail sets status_code label on -1.

this commit adds -1 to the regex match for status_code label.

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✅ zanhsieh
❌ yaskinny
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