ci: clean windows disk space in background

[marcoieni]

Speed up cleaning up disk space by launching the process in the background.
We wait for it to finish before running the build.

Context

The disk space cleanup was introduced in #144305

[marcoieni]

@bors try jobs=msvc,mingw

[rust-bors]

💔 Test for 8cf61b6 failed: CI. Failed jobs:

• try - aarch64-msvc-1 (web logs, extended logs)
• try - aarch64-msvc-2 (web logs, extended logs)
• try - dist-aarch64-msvc (web logs, extended logs)
• try - dist-i686-mingw (web logs, extended logs)
• (and 13 other jobs)

[rust-log-analyzer]

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

tidy check
Checking tidy rustdoc_json...
No error code explanation was removed!
tidy: Skipping binary file check, read-only filesystem
##[error]tidy error: /checkout/src/ci/scripts/free-disk-space-windows-start.py:60: line longer than 100 chars
removing old virtual environment
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'venv'
creating virtual environment at '/checkout/obj/build/venv' using 'python3.10' and 'virtualenv'
Requirement already satisfied: pip in ./build/venv/lib/python3.10/site-packages (25.1.1)
Collecting pip
---
    Uninstalling pip-25.1.1:
      Successfully uninstalled pip-25.1.1
Successfully installed pip-25.2
linting python files
/checkout/src/ci/scripts/free-disk-space-windows-start.py:1:1: EXE001 Shebang is present but file is not executable
/checkout/src/ci/scripts/free-disk-space-windows-wait.py:1:1: EXE001 Shebang is present but file is not executable
Found 2 errors.

python linting failed! Printing diff suggestions:
some tidy checks failed
tidy error: checks with external tool 'ruff' failed
Command `/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/rust-tidy /checkout /checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo /checkout/obj/build 4 /node/bin/npm --extra-checks=py,cpp,js` failed with exit code 1
Created at: src/bootstrap/src/core/build_steps/tool.rs:1636:23
Executed at: src/bootstrap/src/core/build_steps/test.rs:1239:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:01:14
  local time: Tue Aug 12 16:21:40 UTC 2025
  network time: Tue, 12 Aug 2025 16:21:40 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[rust-log-analyzer]

The job x86_64-msvc-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

  SCCACHE_BUCKET: rust-lang-ci-sccache2
  SCCACHE_REGION: us-west-1
  CACHE_DOMAIN: ci-caches.rust-lang.org
##[endgroup]
##[notice]Started free-disk-space cleanup in background (PID=7580); log: C:\a\_temp\free-disk-space.log; pidfile: C:\a\_temp\free-disk-space.pid
##[group]Run src/ci/scripts/setup-environment.sh
src/ci/scripts/setup-environment.sh
shell: C:\Program Files\Git\bin\bash.EXE --noprofile --norc -e -o pipefail {0}
---
fmt: checked 6301 files
tidy check
Checking tidy rustdoc_json...
No error code explanation was removed!
tidy error: C:\a\rust\rust\src\ci\scripts\free-disk-space-windows-start.py:60: line longer than 100 chars
some tidy checks failed
Command `C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0-tools-bin\rust-tidy.exe C:\a\rust\rust C:\a\rust\rust\build\x86_64-pc-windows-msvc\stage0\bin\cargo.exe C:\a\rust\rust\build 4 'C:\Program Files\nodejs\npm'` failed with exit code 1
Created at: src\bootstrap\src\core\build_steps\tool.rs:1636:23
Executed at: src\bootstrap\src\core\build_steps\test.rs:1239:29

Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:02:39
make: *** [Makefile:114: ci-msvc-ps1] Error 1
  local time: Tue Aug 12 16:28:23 CUT 2025
  network time: Tue, 12 Aug 2025 16:28:23 GMT
##[error]Process completed with exit code 2.
Post job cleanup.
[command]"C:\Program Files\Git\bin\git.exe" version