[chore]: Bump github.com/uptrace/bun/dialect/pgdialect

Bumps [github.com/uptrace/bun/dialect/pgdialect](https://github.com/uptrace/bun) from 1.2.8 to 1.2.9.
- [Release notes](https://github.com/uptrace/bun/releases)
- [Changelog](https://github.com/uptrace/bun/blob/v1.2.9/CHANGELOG.md)
- [Commits](https://github.com/uptrace/bun/compare/v1.2.8...v1.2.9)

---
updated-dependencies:
- dependency-name: github.com/uptrace/bun/dialect/pgdialect
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

vendor/github.com/uptrace/bun/query_column_add.go

@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"fmt"
 
+	"github.com/uptrace/bun/dialect/feature"
 	"github.com/uptrace/bun/internal"
 	"github.com/uptrace/bun/schema"
 )
@@ -21,8 +22,7 @@ var _ Query = (*AddColumnQuery)(nil)
 func NewAddColumnQuery(db *DB) *AddColumnQuery {
 	q := &AddColumnQuery{
 		baseQuery: baseQuery{
-			db:   db,
-			conn: db.DB,
+			db: db,
 		},
 	}
 	return q
@@ -133,6 +133,10 @@ func (q *AddColumnQuery) AppendQuery(fmter schema.Formatter, b []byte) (_ []byte
 //------------------------------------------------------------------------------
 
 func (q *AddColumnQuery) Exec(ctx context.Context, dest ...interface{}) (sql.Result, error) {
+	if q.ifNotExists && !q.hasFeature(feature.AlterColumnExists) {
+		return nil, feature.NewNotSupportError(feature.AlterColumnExists)
+	}
+
 	queryBytes, err := q.AppendQuery(q.db.fmter, q.db.makeQueryBytes())
 	if err != nil {
 		return nil, err