Update .devcontainer golang to 1.21.0

[anish749]

building the project using dev containers was failing. I was trying to use codespaces to test.

• go test -golden-update fails without installing npm.

[encore-cla]

All committers have signed the CLA.

[github-actions]

Test Results

  2 files  +    1  227 suites  +65   14m 40s ⏱️ - 11m 26s
722 tests +  163  719 ✅ +  173  3 💤 +3  0 ❌  - 4 
722 runs   - 1 909  719 ✅  - 1 899  3 💤 +3  0 ❌  - 4 

Results for commit 846a262. ± Comparison against base commit 6280377.

This pull request removes 39 and adds 202 tests. Note that renamed tests count towards both.

encr.dev/e2e-tests ‑ TestRun/encore_currentrequest
encr.dev/e2e-tests ‑ TestRun/et_override_user
encr.dev/e2e-tests ‑ TestRun/et_override_user_authdata
encr.dev/e2e-tests ‑ TestRun/experiment_local_secrets_override
encr.dev/e2e-tests ‑ TestRun/fallback_routes
encr.dev/e2e-tests ‑ TestRun/graceful_shutdown
encr.dev/e2e-tests ‑ TestRun/pubsub_method_handler
encr.dev/e2e-tests ‑ TestRun/pubsub_ref
test/svc ‑ TestEndToEndWithApp
test/svc ‑ TestEndToEndWithApp/basic_requests
…

encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/echo
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/invalid
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/raw
encore.dev/appruntime/apisdk/api ‑ TestDescGeneratesTrace/unauthenticated
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/echo
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/invalid
encore.dev/appruntime/apisdk/api ‑ TestDesc_EndToEnd/unauthenticated
encore.dev/appruntime/apisdk/api ‑ TestRawEndpointOverflow
…