build.sh: Change Doxygen command to doc-ci

[crasbe]

With RIOT-OS/RIOT#21300 merged, the command for building the documentation can be changed to doc-ci to generate the documentation with the Doxygen version specified in $(RIOTBASE)/doc/doxygen/Makefile.

With doc-ci, the build system will download the specified Doxygen binaries and use those to generate the documentation instead of relying on the Doxygen version provided by the Ubuntu repositories (which is ooooooold).

Furthermore, it can be updated from within the RIOT repository without changing the build scripts.

See also: RIOT-OS/RIOT#21106

[maribu]

Thx.

You probably also want to take a look at dist/tools/doccheck/check.sh. If you feel like it, you may add this to this PR as well.

[crasbe]

You probably also want to take a look at dist/tools/doccheck/check.sh. If you feel like it, you may add this to this PR as well.

Well I'd have to create a PR in the RIOT repo for that.
That is an interesting thought though, I wonder if that doesn't have other unwanted implications though, for example that on an architecture != x86_64, the make static-test would build Doxygen when the make doc-ci target is used.