fix(ci): set OIDC_COOKIE_SECRET to satisfy production-mode bundle

server/utils/oidc-provider.ts throws at module-load when
OIDC_COOKIE_SECRET is unset and NODE_ENV is 'production'. Vite
substitutes process.env.NODE_ENV as a literal at build time, so
'production' is baked into the .output bundle regardless of the
runtime NODE_ENV=development env. Setting OIDC_COOKIE_SECRET
clears the throw; the value isn't used for real OIDC traffic
in CI since no test exercises the OIDC interaction routes.

.forgejo/workflows/test.yml

@@ -31,6 +31,7 @@ jobs:
       JWT_SECRET: ci-test-jwt-secret
       RESEND_API_KEY: re_ci_dummy_not_used
       HELCIM_API_TOKEN: helcim_ci_dummy_not_used
+      OIDC_COOKIE_SECRET: ci-oidc-cookie-secret-not-secret
       NUXT_PUBLIC_COMING_SOON: 'false'
       NODE_ENV: development
       ALLOW_DEV_TEST_ENDPOINTS: 'true'
@@ -88,6 +89,7 @@ jobs:
       JWT_SECRET: ci-test-jwt-secret
       RESEND_API_KEY: re_ci_dummy_not_used
       HELCIM_API_TOKEN: helcim_ci_dummy_not_used
+      OIDC_COOKIE_SECRET: ci-oidc-cookie-secret-not-secret
       NUXT_PUBLIC_COMING_SOON: 'false'
       NODE_ENV: development
       ALLOW_DEV_TEST_ENDPOINTS: 'true'