ci: speed up the deb package job

The deb job spent ~3m19s in the build step, half of it on work CI does not
need. The package build (via mkdeb.sh) ran the full test suite a second time
with online/network unit tests enabled (~54s), and compressed the large LTO
-dbgsym packages that CI throws away (~48s).

Set DEB_BUILD_OPTIONS=nocheck,noautodbgsym,parallel=N on the CI step only.
nocheck skips debuild's make check, which is redundant here: the build matrix
already runs the suite on every config and mkdeb.sh's own pre-build runs the
offline tests. noautodbgsym drops the -dbgsym packages. parallel uses every
runner core. mkdeb.sh is unchanged, so release builds still build with LTO,
full tests, and debug symbols; only the CI environment differs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Xavier Roche <roche@httrack.com>

.github/workflows/ci.yml

@@ -84,8 +84,16 @@ jobs:
 
       # --unsigned: CI has no GPG key (also skips the release sig/checksums).
       # debuild builds every package, then lintian gates on errors.
+      #
+      # DEB_BUILD_OPTIONS trims work CI does not need (release builds via
+      # mkdeb.sh are untouched): nocheck skips debuild's make check, redundant
+      # here since the build matrix and mkdeb's own pre-build already run the
+      # suite; noautodbgsym drops the -dbgsym packages whose LTO payloads are
+      # slow to compress and that CI never ships; parallel uses every core.
       - name: Build Debian packages
-        run: bash tools/mkdeb.sh --unsigned --no-release-artifacts
+        run: |
+          export DEB_BUILD_OPTIONS="nocheck noautodbgsym parallel=$(nproc)"
+          bash tools/mkdeb.sh --unsigned --no-release-artifacts
 
   dco:
     name: DCO sign-off