[jdk21u] RFR: 8313701: GHA: RISC-V should use the official repository for bootstrap [v3]

[Aleksey Shipilev]

> Clean backport to improve GHA stability.
> 
> Additional testing:
>  - [ ] GHA

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8313701-gha-riscv-official
 - Merge branch 'master' into JDK-8313701-gha-riscv-official
 - Backport 538f9557b87f750264231f04bfbc91d15f8af8c0

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

Changes:
  - all: https://git.openjdk.org/jdk21u/pull/78/files
  - new: https://git.openjdk.org/jdk21u/pull/78/files/770ecad5..7b726918

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk21u&pr=78&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk21u&pr=78&range=01-02

  Stats: 328 lines in 24 files changed: 260 ins; 1 del; 67 mod
  Patch: https://git.openjdk.org/jdk21u/pull/78.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/78/head:pull/78

PR: https://git.openjdk.org/jdk21u/pull/78