Drop Bazel 6 from BCR presubmits (#631)

Forgot to update it in #613

.bcr/gazelle/presubmit.yml

diff --git a/.bcr/gazelle/presubmit.yml b/.bcr/gazelle/presubmit.yml
index 4daf8f9..f8a7e79 100644
--- a/.bcr/gazelle/presubmit.yml
+++ b/.bcr/gazelle/presubmit.yml
@@ -8,9 +8,9 @@
   - ubuntu2404
   - windows
   bazel:
+  - 9.x
   - 8.x
   - 7.x
-  - 6.x
 tasks:
   verify_build_targets:
     name: "Verify build targets"

.bcr/presubmit.yml

diff --git a/.bcr/presubmit.yml b/.bcr/presubmit.yml
index d420eb1..73d47dc 100644
--- a/.bcr/presubmit.yml
+++ b/.bcr/presubmit.yml
@@ -8,9 +8,9 @@
   - ubuntu2404
   - windows
   bazel:
+  - 9.x
   - 8.x
   - 7.x
-  - 6.x
 tasks:
   verify_build_targets:
     name: "Verify build targets"