ci: add markdown link check job

This should prevent us reintroducing broken markdown links.

It does not test "online" (external) links, only those within this repo.
Both relative and absolute links are parsed successfully if they
resolve.

.github/workflows/ci.yml

@@ -308,3 +308,13 @@ jobs:
  BITCOINFUZZ: "${{ github.workspace}}\\src\\fuzz.exe"
  shell: cmd
  run: py -3 test\fuzz\test_runner.py --par %NUMBER_OF_PROCESSORS% --loglevel DEBUG %RUNNER_TEMP%\qa-assets\fuzz_seed_corpus
+ check-md-links:
+ name: "Check markdown links"
+ runs-on: ubuntu-latest
+ steps:
+ - name: Checkout
+ uses: actions/checkout@v4
+ - name: Markup Link Checker (mlc)
+ uses: becheran/[email protected]
+ with:
+ args: --offline --ignore-path "./doc/release-notes","./doc/README_doxygen.md","./.github","./src/crc32c","./src/crypto","./src/leveldb","./src/minisketch","./src/secp256k1" --root-dir ./ ./