Disable rmake test `inaccessible-temp-dir` on riscv64
In https://github.com/rust-lang/rust/pull/126279 the `inaccessible-temp-dir` test was moved to rmake, I followed up with a 'fix' derived from https://github.com/rust-lang/rust/pull/126355 in https://github.com/rust-lang/rust/pull/126707.
That 'fix' was misguided and hiding the true issue of the linker being incorrect for `riscv64gc-unknown-linux-gnu` (addressed in https://github.com/rust-lang/rust/pull/126916).
Unfortunately, even with the linker fixed, this test doesn't work. I asked myself why this appeared to work on other platforms and investigated why. Both the containers for `armhf-gnu` and `riscv64gc` run their tests as `root` and have `NO_CHANGE_USER` set:
553a69030e/src/ci/docker/host-x86_64/disabled/riscv64gc-gnu/Dockerfile (L99)
This means the tests are run as `root`. As `root`, it's perfectly normal and reasonable to violate permission checks this way:
```bash
$ sudo mkdir scratch
$ sudo chmod o-w scratch
$ sudo mkdir scratch/backs
$
```
Because of this, this PR makes the test ignored on `riscv64gc` for now.
As an alternative, I believe the best long-term strategy would be to not run the tests as `root` for this job.
## Testing
> [!NOTE]
> `riscv64gc-unknown-linux-gnu` is a [**Tier 2 with Host Tools** platform](https://doc.rust-lang.org/beta/rustc/platform-support.html), all tests may not necessarily pass! This change should only ignore `inaccessible-temp-dir` and not affect other tests.
You can test out the job locally:
```sh
mv src/ci/docker/host-x86_64/disabled/riscv64gc-gnu src/ci/docker/host-x86_64/riscv64gc-gnu
DEPLOY=1 ./src/ci/docker/run.sh riscv64gc-gnu
```
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