build: hard code doctool in test-doc target

This commit removes the usage of the CI_DOC variable in the test-doc
recipe and specifies the doctool argument to tools/test.py explicitly.

The motivation for this is that the build is taking longer time and
this is mostly due to tests being run twice as the CI_DOC
variable will be empty in most cases (when not using --without-ssl).

This change was introduced with/after Commit
9039af8 ("build: skip test-ci doc
targets if no crypto") and while I though it might make sense to change
the setting of CI_DOC I not sure about the implications that might have
to our CI environment. It currently looks like this:

ifeq ($(node_use_openssl), false)
        CI_DOC := doctool
else
        CI_DOC =
endif

Which is setting CI_DOC to doctool if there is no crypto support which
not available. But perhaps this should be be the other way around,
changing the order or updating condition to be true.

PR-URL: #29375
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Makefile

@@ -604,7 +604,7 @@ test-doc: doc-only ## Builds, lints, and verifies the docs.
 		echo "Skipping test-doc (no crypto)"; \
 	else \
 		$(MAKE) lint; \
-		$(PYTHON) tools/test.py $(PARALLEL_ARGS) $(CI_DOC); \
+		$(PYTHON) tools/test.py $(PARALLEL_ARGS) doctool; \
 	fi
 
 test-known-issues: all