RFR: 8313701: GHA: RISC-V should use the official repository for bootstrap

[Aleksey Shipilev]

RISC-V is now the [official Debian architecture](https://lists.debian.org/debian-riscv/2023/07/msg00053.html). This means that the official repository is slowly building up the package set, while the old debian-ports repo is [slowly rotting](https://lists.debian.org/debian-riscv/2023/08/msg00007.html). For futureproof-ness, we want to bootstrap from the official repo going forward.

Additional testing:
 - [ ] GHA

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/15149/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15149&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313701
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15149.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15149/head:pull/15149

PR: https://git.openjdk.org/jdk/pull/15149