Point the source-tree links at maven-3.10.x rather than master

[slachiewicz]

Four links on the Core ITs Suite pages address files by way of this repository's master branch. Master was emptied to a four-file stub when the IT tree moved into apache/maven (commit "Branch 3.10.x created"), so three of the four now return 404, and the fourth reaches a signpost README rather than the instructions the sentence promises.

Base branch: maven-3.10.x.

Stacked on #433 — the pages only exist in Markdown form after that PR, so this branch is built on top of it and the diff shown here includes its two commits until it merges. Merge #433 first; this PR's own change is the single commit Point the source-tree links at maven-3.10.x rather than master, two files, four lines.

What changes

link	before	after
README.md	blob/master/README.md — 200, but master's README is now just a list of surviving branches	blob/maven-3.10.x/README.md
default settings.xml	blob/master/core-it-suite/src/test/resources-filtered/settings.xml — 404	blob/maven-3.10.x/…
bootstrap.txt	blob/master/core-it-suite/src/test/**resources**/bootstrap.txt — 404	blob/maven-3.10.x/core-it-suite/src/test/**resources-filtered**/bootstrap.txt
bootstrap projects	tree/master/core-it-suite/src/test/resources/bootstrap — 404	tree/maven-3.10.x/…

Two notes on the choices:

• bootstrap.txt was also addressing the wrong directory, independently of the branch — the file is under src/test/resources-filtered, not src/test/resources, so that link would have been dead on any ref. Both errors are fixed together.
• maven-3.10.x rather than a tag or master. The branch is what this site is built from, so the page and the tree it describes stay in step; a tag would freeze and drift. Master is what got us here, and it got there by being emptied rather than by being a branch. The bare repository-root link ("the official Core ITs Suite repository") is left alone — it resolves and is meant to name the repository, not a ref.

Verification

• Every rewritten URL fetched with curl -L: all four return 200, url_effective unchanged, so no redirect to a repository root. The three replaced ones were confirmed 404 first.
• mvn -N site in core-it-suite, exit 0, compared against the build from Port the site documentation from APT to Markdown #433's head: the four link targets are the only difference in the generated pages.

Not addressed here

<scm><tag>master</tag></scm> in the POM, with <url>…/tree/${project.scm.tag}</url>, points the generated "edit this page" link on every page and the source-repository report into the same emptied master. That is release metadata rather than documentation, and maven-3.9.x carries it identically, so it wants a committer's decision across both branches rather than a drive-by change in a docs PR.

_{Drafted with Claude — please verify}