build system: use env var for bazel version in CI (#1098)

.bazeliskrc

@@ -0,0 +1 @@
+USE_BAZEL_VERSION=6.x

.bazelversion

@@ -1 +0,0 @@
-6.3.2

.github/workflows/bazel.yml

@@ -16,3 +16,5 @@ jobs:
     - uses: actions/checkout@v4
     - run: bazelisk test --config=ci ...
       working-directory: test
+      env:
+        USE_BAZEL_VERSION: 6.x

WORKSPACE.bazel

@@ -0,0 +1 @@
+# SEE MODULE.bazel