Print rerun command for failed parallel_rspec shards (#5339)

Add --verbose-rerun-command to the parallel_rspec invocations so a
failing shard prints a copy-pasteable command with its exact file list
and seed. This makes order-dependent flakes reproducible locally, since
RSpec order depends on both the seed and the shard's file set and the
latter was not previously recoverable from CI output.

The flag only emits output on failure, so green runs are unaffected.

Author: philippthun

lib/tasks/spec.rake

@@ -47,6 +47,7 @@ namespace :spec do
       #{env_vars} bundle exec parallel_rspec \
       --test-options '--order rand #{rspec_profile_option} --format progress --format ParallelTests::RSpec::RuntimeLogger --out tmp/parallel_runtime_rspec_main.log' \
       --runtime-log tmp/parallel_runtime_rspec_main.log \
+      --verbose-rerun-command \
       --single spec/integration/ \
       --single spec/acceptance/ \
       --isolate \
@@ -61,6 +62,7 @@ namespace :spec do
       #{env_vars} bundle exec parallel_rspec \
       --test-options '--order rand #{rspec_profile_option} --format progress --format ParallelTests::RSpec::RuntimeLogger --out tmp/parallel_runtime_rspec_migrations.log' \
       --runtime-log tmp/parallel_runtime_rspec_migrations.log \
+      --verbose-rerun-command \
       -- spec/migrations
     CMD
     sh command