Feat: Automatically trigger integration tests scoped to modified dialects

[erindru]

This PR:

• Introduces automatic triggers for the integration tests. There are two ways:
  • Use a /integration-tests indicator in your PR description or comment. For a specific dialect or dialects, use /integration-tests dialects=duckdb,bigquery
  • If there is no /integration-tests indicator, then the script looks at the changed files. If any of the file names contain a dialect supported by the test suite, the tests will run for that dialect
  • It's based on a Python script that inspects the GitHub event payload and writes specific output variables depending on what it finds
• Updates the summary comment if it already exists rather than publishing a new one each time

/integration-tests dialect=bigquery

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:erin/integration-test-automation, sqlglot version: erin/integration-test-automation)
• baseline (main, sqlglot version: 28.1.1.dev71)

⚠️ Limited to dialects: bigquery

By Dialect

dialect	main	sqlglot:erin/integration-test-automation	difference	links
bigquery -> bigquery	651/651 passed (100.0%)	651/651 passed (100.0%)	No change	full result / delta
bigquery -> duckdb	459/650 passed (70.6%)	458/650 passed (70.5%)	⬇ regressed by 0.2%	full result / delta

Overall

main: 1301 total, 1110 passed (pass rate: 85.3%), sqlglot version: 28.1.1.dev71

sqlglot:erin/integration-test-automation: 1301 total, 1109 passed (pass rate: 85.2%), sqlglot version: erin/integration-test-automation

Difference: ⬇ regressed by 0.1%