docs: fix custom trigger filtering — replace exit 1 with job-based graceful skip

[Copilot]

Using exit 1 in a pre-agent step to filter triggers marks the entire workflow run as failed, cluttering the Actions tab with red X's and spuriously firing the Workflow Failure issue mechanism.

Changes

• Job-based filter pattern (primary): Replace the exit 1 step anti-pattern with a deterministic filter job that sets a boolean output and never exits non-zero. The if: frontmatter field references the output; the compiler wires the filter job as a dependency of activation so non-matching runs are skipped, not failed.

jobs:
  filter:
    runs-on: ubuntu-latest
    outputs:
      should-run: ${{ steps.check.outputs.result }}
    steps:
      - id: check
        env:
          LABELS: ${{ toJSON(github.event.issue.labels.*.name) }}
        run: |
          if echo "$LABELS" | grep -q '"bug"'; then
            echo "result=true" >> "$GITHUB_OUTPUT"
          else
            echo "result=false" >> "$GITHUB_OUTPUT"
          fi

if: needs.filter.outputs.should-run == 'true'

• Simple context conditions: Added subsection showing direct if: usage (no custom job needed) for conditions expressible from GitHub Actions context alone.
• Query-based filtering: Added subsection pointing to skip-if-match: / skip-if-no-match: as the idiomatic mechanism when the filter can be expressed as a GitHub search query — both produce the same skipped-not-failed outcome.

[Copilot]

Pull request overview

Updates the “Custom Trigger Filtering” documentation to avoid failing workflows when a trigger doesn’t match, by describing skip-based filtering patterns instead of using exit 1.

Changes:

• Replaces the exit 1 trigger-filtering example with a job output + workflow-level if: pattern.
• Adds a “Simple Context Conditions” subsection showing direct if: usage without a custom job.
• Adds a “Query-Based Filtering” subsection pointing to skip-if-match / skip-if-no-match.

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