chore: bump buildifier to 6.1.0 (#1152)

Bump the buildifier to the latest version in pre-commit and CI at the
same time.

Related to #1148 and #1151.

.bazelci/presubmit.yml

diff --git a/.bazelci/presubmit.yml b/.bazelci/presubmit.yml
index f10a648..0e9feab 100644
--- a/.bazelci/presubmit.yml
+++ b/.bazelci/presubmit.yml
@@ -16,7 +16,7 @@
 buildifier:
   # keep these arguments in sync with .pre-commit-config.yaml
   # Use a specific version to avoid skew issues when new versions are released.
-  version: 6.0.0
+  version: 6.1.0
   warnings: "all"
 .minimum_supported_version: &minimum_supported_version
   # For testing minimum supported version.

.pre-commit-config.yaml

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 9403dd5..be5f47f 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -17,7 +17,7 @@
 # See https://pre-commit.com/hooks.html for more hooks
 repos:
   - repo: https://github.com/keith/pre-commit-buildifier
-    rev: 6.0.0
+    rev: 6.1.0
     hooks:
       - id: buildifier
         args: &args