fix: resolve links correctly when book contains exactly one chapter (#…

…101)

Pandoc's `--file-scope` option [only takes effect if there are at least
two files](https://pandoc.org/MANUAL.html#option--file-scope[), so if
there is only one file, links will not be adjusted correctly. In this
case, add an additional empty dummy file as input to convince Pandoc to
perform the link adjustment.

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - name: Install dependencies
         run: ./scripts/install-ci-deps
       - name: nextest
-        run: cargo nextest run
+        run: cargo nextest run --run-ignored all
       - name: doctest
         run: cargo test --doc
       - name: Archive rendered books