chore: add changeset for skipIfActive feature

Author: eni9889

.changeset/skip-if-active.md

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+---
+"@trigger.dev/core": minor
+---
+
+Add `skipIfActive: boolean` option to `tasks.trigger()` and batch items. When set (along with at least one `tag`), the server checks for an in-flight (non-terminal) TaskRun in the same environment with matching `taskIdentifier` and all of the supplied tags. If found, the trigger is a no-op and the existing run is returned with `isCached: true` + new `wasSkipped: true` flag — no new run, no queue entry.
+
+Purpose: a first-class drop-on-conflict primitive for cron-style orchestrators that poll at a fixed cadence and should skip duplicate triggers without building a queue backlog (unlike `concurrencyKey`) or caching successful completions (unlike `idempotencyKey`).