Bug 1751515 - Part 3: Do not install artifact test archive when `--disable-tests`. r=firefox-build-system-reviewers,glandium

When consuming artifacts from `Bs` jobs, there is no test archive.
The consumer still needs to specify "no tests", but this at least
allows the artifact build to proceed.

Differential Revision: https://phabricator.services.mozilla.com/D136930

Makefile.in

@@ -111,7 +111,7 @@ verbose_flag = -v
 endif
 
 recurse_artifact:
-	$(PYTHON3) $(topsrcdir)/mach --log-no-times artifact install$(if $(MOZ_ARTIFACT_BUILD_SYMBOLS), --symbols$(addprefix =,$(filter full,$(MOZ_ARTIFACT_BUILD_SYMBOLS)))) $(verbose_flag)
+	$(PYTHON3) $(topsrcdir)/mach --log-no-times artifact install$(if $(MOZ_ARTIFACT_BUILD_SYMBOLS), --symbols$(addprefix =,$(filter full,$(MOZ_ARTIFACT_BUILD_SYMBOLS)))) $(if $(ENABLE_TESTS),,--no-tests) $(verbose_flag)
 
 ifdef MOZ_EME_WIN32_ARTIFACT
 recurse_win32-artifact: