Update silences.md (#38834)
Update silences.md (#38834)

* Update silences.md

minor correction in not equals regex

* Update docs/sources/alerting/unified-alerting/silences.md

Co-authored-by: achatterjee-grafana <5ed7255a3b2540ccce8f5b30c47e4a93678b261d@users.noreply.github.com>
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