Update the .bazelversion and support matrix for 6.3.1

PiperOrigin-RevId: 552558168
Change-Id: I2c10ddbd8c7e1adb5a9889ac30a713fa58933999
diff --git a/.bazelversion b/.bazelversion
index 798e389..dc0208a 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-6.3.0
+6.3.1
diff --git a/site/en/release/index.md b/site/en/release/index.md
index d937586..e2773cd 100644
--- a/site/en/release/index.md
+++ b/site/en/release/index.md
@@ -84,7 +84,7 @@
 | LTS release | Support stage | Latest version | End of support |
 | ----------- | ------------- | -------------- | -------------- |
 | Bazel 7 | Rolling| [Check GitHub release page](https://github.com/bazelbuild/bazel/releases){: .external} | N/A |
-| Bazel 6 | Active | [6.3.0](https://github.com/bazelbuild/bazel/releases/tag/6.3.0){: .external} | Dec 2025 |
+| Bazel 6 | Active | [6.3.1](https://github.com/bazelbuild/bazel/releases/tag/6.3.1){: .external} | Dec 2025 |
 | Bazel 5 | Maintenance | [5.4.1](https://github.com/bazelbuild/bazel/releases/tag/5.4.1){: .external} | Jan 2025 |
 | Bazel 4 | Maintenance | [4.2.4](https://github.com/bazelbuild/bazel/releases/tag/4.2.4){: .external} | Jan 2024 |