package all `.eo` files from `eo-runtime/src/test/eo/` into a new JAR also released to Maven Central

[yegor256]

Motivated by https://github.com/objectionary/normalizer/issues/478

Let's package all test-*.eo files into a new JAR, with a classifier:

<dependency>
  <groupId>org.eolang</groupId>
  <artifactId>eo-runtime</artifactId>
  <version>0.0.0</version>
  <classifier>tests</classifier>
</dependency>

This will help all other projects to reuse our tests.