Change `http://` to `https://` in our ASL2 copyright header?

### Description

Randomly, while [grep'ing for `http` in our sources to locate links to external papers that inspired important changes in Lucene](https://github.com/apache/lucene/pull/14078#issuecomment-2569246977), I noticed that our standard `Apache Software License version 2.0` copyright header still uses the non-SSL (`http://`) link.

Should we update that to `https://`? Would that show that Lucene devs take security seriously or so ("lead by example")? If you load the [non-SSL url](http://www.apache.org/licenses/LICENSE-2.0) it redirects anyways to the SSL version.

Apache's [official guidelines on the copyright header text specifically state that `https` is acceptable](https://www.apache.org/legal/src-headers.html#headers), though the copy/paste text sample given there is non-SSL.

Curiously, a couple source files in Lucene *do* use the `https://` URL in the copyright header! [`gradlew.bat`](https://github.com/apache/lucene/blob/main/gradlew.bat#L8) and [`gradlew`](https://github.com/apache/lucene/blob/main/gradlew#L10), cool.

Using GitHub's search, I count ~[43.8K source files under the Apache org that use the SSL URL](https://github.com/search?q=org%3Aapache%20%22https%3A%2F%2Fwww.apache.org%2Flicenses%2FLICENSE-2.0%22&type=code), and [~1.3M source files that do not](https://github.com/search?q=org%3Aapache+%22http%3A%2F%2Fwww.apache.org%2Flicenses%2FLICENSE-2.0%22&type=code)! We could be early adopters and join the ~3.2% of Apache source code that does use the SSL link!

Search the repository for the standard Apache Software License header and compare the existing http:// URL with the https:// versions in gradlew and gradlew.bat. Determine the complete set of source files that should use the secure URL, then verify that the resulting search no longer finds outdated headers without changing unrelated links.

Written by the indexing model from the issue text.