RFR: Update gradle to version 8.11.1 and fix GitHub actions [v3]

[Jorn Vernee]

> Currently the github actions are failing because we depend on versions of the JDK (17 and 22), that are no longer available through the oracle/setup-java github action.
> 
> There are 2 barriers to upgrading these JDK version to ones that are supported:
> 1. The current version of Gradle we are using doesn't run on newer Java versions
> 2. Due to our use of `--enable-preview` and `--release 22` to compile, we are locked to JDK 22.
> 
> This PR updates Gradle to the latest version, which supports running on Java 23. It also drops the `--enable-preview` flag from compilation, which is not actually needed, allowing us to compile using JDK 23 as well. Both these changes then allow us to use JDK 23 to run Gradle, and as a toolchain JDK, in the GitHub actions. Since JDK 23 is available through oracle/setup-java, GitHub actions will work again.

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Add gradle wrapper validation step

-------------

Changes:
  - all: https://git.openjdk.org/jextract/pull/264/files
  - new: https://git.openjdk.org/jextract/pull/264/files/7def72ae..a4ff0095

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jextract&pr=264&range=02
 - incr: https://webrevs.openjdk.org/?repo=jextract&pr=264&range=01-02

  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jextract/pull/264.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/264/head:pull/264

PR: https://git.openjdk.org/jextract/pull/264