chore(gradle): bump org.apache.arrow.adbc:adbc-driver-flight-sql from 0.19.0 to 0.21.0 (#7396)

Bumps org.apache.arrow.adbc:adbc-driver-flight-sql from 0.19.0 to 0.21.0.

---
updated-dependencies:
- dependency-name: org.apache.arrow.adbc:adbc-driver-flight-sql
  dependency-version: 0.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-adbc = "0.19.0"
+adbc = "0.21.0"
 airlift = "2.0.2"
 arrow = "18.3.0"
 autoservice = "1.1.1"