Fix auth key casing for multi-word translated labels

[wwenrr]

Summary

Fixes the capitalization regression reported in #5835 when human_attribute_name returns a multi-word string (e.g. "Email Address").

Previously this produced:

• Invalid email Address or password.

With this change it produces:

• Invalid email address or password.

What changed

• In Devise::FailureApp#i18n_message, when building authentication_keys:
  • Keep existing behavior for single-word labels (downcase_first fallback)
  • Downcase the whole string for multi-word labels (human_key.include?(" ") ? human_key.downcase : ...)

This preserves behavior for values like "E-Mail" while fixing awkward capitalization for values like "Email Address".

Tests

Added coverage in test/failure_app_test.rb:

• preserves translation capitalization after auth key replacement

Verification run (manual)

I ran the failure app test file locally in a clean Docker Ruby 3.4 environment:

docker run --rm -v "$PWD":/app -w /app ruby:3.4 bash -lc '
  apt-get update >/dev/null && \
  apt-get install -y --no-install-recommends build-essential git pkg-config libsqlite3-dev >/dev/null && \
  bundle install >/dev/null && \
  bin/test test/failure_app_test.rb
'

Result: 45 runs, 91 assertions, 0 failures, 0 errors, 0 skips.

[carlosantoniodasilva]

Thanks! This may fix the immediate problem (and I'll probably apply it soon), but I'm afraid we're going to be playing whack-a-mole with this translation thing 😅

Anyway, let's give it another try before I decide to revert it all back and try a different approach.

Note: there are failures for mongoid, it needs to have translations stored as well.

[wwenrr]

Root cause: the new capitalization test only set activerecord translation, but this matrix failures are under DEVISE_ORM=mongoid so it resolved to default "email". I pushed a fix to include matching mongoid.attributes.user.email translation in the test setup (commit a7cd6af). Please re-run CI.