CI: test on Bazel 7.x and 9.x only (skip 8.x)

Bazel 8 is expected to work (it is between two tested versions), so
there is no need to test it explicitly.

Signed-off-by: Steffen Smolka <steffen.smolka@gmail.com>
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: smolkaj

.github/workflows/bazel-build.yml

@@ -21,7 +21,7 @@ jobs:
         # We trust that things also work for versions in the middle.
         os: [ubuntu-22.04, ubuntu-latest]
         # See Bazelisk README for legal values.
-        bazel_version: [7.x, 8.x, 9.x]
+        bazel_version: [7.x, 9.x]
       # Don't abort other runs when one of them fails, to ease debugging.
       fail-fast: false