[ci] Use the correct flag to set the ruby version

Author: shs96c

.github/workflows/ci-rbe.yml

@@ -9,6 +9,7 @@ jobs:
     name: Test
     uses: ./.github/workflows/bazel.yml
     with:
-      name: Cache
+      name: All RBE tests
       cache-key: rbe
+      ruby-version: jruby-9.4.2.0
       run: ./scripts/github-actions/ci-build.sh

scripts/github-actions/ci-build.sh

@@ -8,9 +8,6 @@ set -x
 ./scripts/format.sh
 git diff --exit-code
 
-# We want to use a pre-built Ruby version
-echo 'RUBY_VERSION = "jruby-9.4.2.0"' >rb/ruby_version.bzl
-
 # The NPM repository rule wants to write to the HOME directory
 # but that's configured for the remote build machines, so run
 # that repository rule first so that the subsequent remote