fix(qwik-city): allow qwik to process .mdx files #16493

Job	Run time
Lint Package	1m 2s
Setup	13s
Build Qwik	0s
Build optimizer ${{ matrix.settings.target }}	0s
Bundle Qwik	12s
Build Other Packages	1m 37s
Build Docs	2m 3s
Build Insights	42s
Unit Tests	41s
E2E Tests (ubuntu-latest, chromium)	7m 4s
E2E Tests (macos-latest, webkit)	6m 4s
E2E CLI Tests (ubuntu-latest)	1m 0s
E2E Tests (windows-latest, chromium)	9m 37s
E2E CLI Tests (macos-latest)	1m 58s
E2E CLI Tests (windows-latest)	3m 40s
All requirements are met	1s
Release	42s
Trigger Qwik City E2E	0s
	36m 36s

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