Use documentation formatter for rspec in devcontainer CI

`devcontainers/ci@v0.3` runs `runCmd` via `docker exec -t`, which
gives the container a TTY. Ruby on a TTY sets `STDOUT.sync = true`,
so rspec's progress formatter (which prints `.` per example with no
newline) is flushed per character. The action's log capture treats
each flush as a separate line, so a full spec run ends up with
thousands of timestamped lines that each contain a single
ANSI-wrapped dot.

Pass `SPEC_OPTS="--format documentation"` only for this workflow's
`rake spec` invocation. The documentation formatter prints one full
line per example (via `puts`, which includes a newline), so the
action records one tidy log line per test instead of one per dot.
Local `.rspec` is unchanged.

`.rspec` is shared with local development and other workflows
(`test.yml`, `test_11g*.yml`, `test_gemfiles.yml`, `ruby_head.yml`,
`jruby_head.yml`, `truffleruby.yml`) which run rspec without the
docker-exec TTY layer and where progress dots batch correctly.
Limiting the override to the devcontainer workflow avoids changing
what everyone else sees locally. Mirrors rsim/oracle-enhanced#2802.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yahonda

.github/workflows/devcontainer.yml

@@ -21,5 +21,5 @@ jobs:
             uname -a
             lsb_release -a
             ruby --version
-            bundle exec rake spec
+            SPEC_OPTS="--format documentation" bundle exec rake spec
             bundle exec rubocop