EM cannot resolve webjars artifacts created with the webjar extension with the Maven repository handler

Reproduction step:

• build xwiki-platform-distribution-jetty-hsqldb and unzip it
• Go in webapps/xwiki/WEB-INF/lib/
• remove xwiki-platform-tree-webjar and xwiki-platform-captcha-jcaptcha-webjar jars
• Start the wiki and install the standard flavor

Expected result:

• the flavor is properly installed, the missing webjars are resolved through the Maven repository

Obtained result:

• the EM does not manage to resolve the webjar, the following error is displayed during the install step (install plan is OK):

   Could not find artifact org.xwiki.platform:xwiki-platform-tree-webjar:webjar:11.10.1-20191203.083548-14 in maven-xwiki-snapshot (http://nexus.xwiki.org/nexus/content/groups/public-snapshots)