CI: repo packages have higher priority than built ones during build test

Description:

Tests for #14696 are installing dependencies packages from repo instead of using the ones available during the build.
When a makefile generates both pkgA-boo and pkgA-foo and pkgA-boo requires pkgA-foo, it looks like the CI scripts gets the pkgA-foo from repository instead of using the just compiled one.

There are many cases but I'll focus on ruby-singleton:

Testing package ruby-erb in version 3.0.0 from ruby
...
Installing ruby-singleton (2.7.2-1) to root...
Downloading https://downloads.openwrt.org/snapshots/packages/aarch64_cortex-a53/packages/ruby-singleton_2.7.2-1_aarch64_cortex-a53.ipk
...
Testing package ruby-singleton in version 3.0.0 from ruby
Upgrading ruby-singleton on root from 2.7.2-1 to 3.0.0-1...
Removing obsolete file /usr/lib/ruby/2.7/singleton.rb.
Removing obsolete file /usr/lib/ruby/2.7/singleton/version.rb.
Removing obsolete file /usr/lib/ruby/gems/2.7/specifications/default/singleton-0.1.0.gemspec.
Configuring ruby-singleton.
No test.sh script available
Removing package ruby-drb from root...
Removing package ruby-rake from root...
Removing package ruby-singleton from root...
...

Maybe I could use EXTRA_DEPENDS for locking the version requirements to force the selection of a specific version but OpenWrt does not seem to heavily use version dependencies.