build(java): bump Spark 4 from 4.1.1 to 4.1.2 (#8813)

## Rationale for this change

Spark 4.1.2 is the latest maintenance release of the 4.1 line on Maven
Central,
containing bug fixes over 4.1.1. Keeping the Spark 4 dependency current
picks up those
fixes for the `vortex-spark_2.13` builds. Companion to #8812, which
bumps the Spark 3
line.

## What changes are included in this PR?

A one-line version bump in `java/gradle/libs.versions.toml`: `spark4 =
"4.1.1"` →
`spark4 = "4.1.2"`. No code changes.

Verified locally against 4.1.2 with `:vortex-spark_2.13:test`: 120 tests
ran, all
passed except `VortexDataSourceS3MockTest`, which failed only because
the local Docker
daemon was not running (Testcontainers infrastructure requirement,
unrelated to the
Spark version).

## What APIs are changed? Are there any user-facing changes?

None. Spark 4.1.2 is a drop-in maintenance upgrade; no connector code or
public API
is touched.

Signed-off-by: jackylee <qcsd2011@gmail.com>

Author: jackylee-ch

java/gradle/libs.versions.toml

@@ -13,7 +13,7 @@ nopen = "1.0.1"
 roaringbitmap = "1.6.14"
 slf4j = "2.0.18"
 spark3 = "3.5.9"
-spark4 = "4.1.1"
+spark4 = "4.1.2"
 s3mock = "5.0.0"
 testcontainers-jupiter = "1.21.4"