ci: javadoc.sh fails on scylla-4.x, coverage-report cannot resolve integration-tests #1111

docs/_utils/javadoc.sh fails on scylla-4.x, so adding that branch to BRANCHES (#1079) would publish it — and stable, since #1079 also makes it LATEST_VERSION — with an empty api/.

Reproduction

JDK 11 (what javadoc-multiversion.sh selects for any branch not in its allowlist), clean checkout of scylla-4.x at f597f09a63:

$ ./docs/_utils/javadoc.sh
...
[INFO] Java driver ... - coverage report FAILURE [  0.012 s]
[INFO] BUILD FAILURE
[ERROR] Failed to execute goal on project java-driver-coverage-report: Could not resolve dependencies
        for project com.scylladb:java-driver-coverage-report:pom:4.19.2.2-SNAPSHOT
[ERROR] dependency: com.scylladb:java-driver-integration-tests:jar:4.19.2.2-SNAPSHOT (compile)
[ERROR] 	Could not find artifact com.scylladb:java-driver-integration-tests:jar:4.19.2.2-SNAPSHOT
$ echo $?
1

docs/_build/dirhtml/api/ is never created — javadoc.sh:2 is set -euo pipefail, so the script dies at the mvn javadoc:javadoc on line 15, before the copy on line 34. Core's javadoc had already been generated into core/target/reports/apidocs; it is simply never moved.

Cause

• coverage-report/pom.xml:86-88 declares a compile dependency on java-driver-integration-tests.
• integration-tests/pom.xml:359-361 sets maven-install-plugin <skip>true</skip>, so javadoc.sh:5's mvn install -DskipTests never puts that jar in the local repository.
• javadoc.sh:15's mvn javadoc:javadoc is a standalone goal invocation, so coverage-report resolves the dependency from the repository rather than from reactor output, and does not find it.

Not a local artifact: docs-pages.yml restores no maven cache, so every publish run starts from a clean ~/.m2 and hits the same path.

Why it has not bitten yet

coverage-report is newer than every branch currently in BRANCHES — the module is absent from scylla-4.19.0.x, scylla-4.18.1.x and scylla-4.15.0.x. All 16 published branches build their javadoc fine, which is why run 35243119768 was green with 17/17 populated api/ directories. scylla-4.x is the first branch to carry the module, and #1079 is what would first build it.

Fix

Restrict the javadoc build to the module that is actually published, which is what #1107 already proposes for unrelated reasons:

-mvn javadoc:javadoc -T 1C
+mvn javadoc:javadoc -pl core -T 1C

Verified on scylla-4.x under JDK 11: BUILD SUCCESS, core/target/reports/apidocs with 728 files including index.html, from a cleaned output directory. javadoc.sh:5's mvn install already populates everything core needs, so no -am is required.

Blocks #1079 / DRIVER-1036. Related: #1107 (same change), #1101 (the guard that would at least make this loud), #1103 (no pre-merge coverage of this path).