Check Spotless formatting by default build

[ascheman]

Detected in the course of support-and-care/maven-support-and-care#77.

This PR should not be merged before

• Apply spotless re-formatting plexus-archiver#367
• Apply spotless re-formatting plexus-compiler#429
• Apply spotless re-formatting plexus-i18n#19
• Apply spotless re-formatting plexus-interactivity#68
• Apply spotless re-formatting plexus-interpolation#81
• Apply spotless re-formatting plexus-sec-dispatcher#100
• Apply spotless re-formatting modello#488
• Apply spotless re-formatting plexus-xml#59
• Apply spotless re-formatting plexus-classworlds#123

[slachiewicz]

Why is this not the default?

[slawekjaranowski]

should be done in parent pom.
please look at Maven parent.

[ascheman]

If it was active by default, the GH action builds of the mentioned projects should have failed, right?
The parent POM uses the check in a particular profile (format-check), which is activated when the CI environment variable is set.

Should I change the PR to set this environment variable or perhaps to activate the Maven profile?