enhance: test on Windows and fix what it found (#1348)

Adds a weekly and on-demand workflow that runs the cross-compiled tests on Windows Server 2025 Core in a [dockur/windows](https://github.com/dockur/windows) QEMU VM, and fixes the Windows bugs it found in host and UNC paths, env handling, shell quoting, post-task scripts, health checks, checkout, action symlinks, step summaries, Git client certificates and docker mode from a Windows host.

Host-mode steps now emit UTF-8, `bash` falls back to Git's bash instead of the WSL launcher, the runner can run as a native Windows service, steps can keep background helpers with `RUNNER_TRACKING_ID`, and Windows arm64 binaries are released.

Fixes: https://gitea.com/gitea/runner/issues/1339
Fixes: https://gitea.com/gitea/runner/issues/637
Fixes: https://gitea.com/gitea/runner/issues/1172
Fixes: https://gitea.com/gitea/runner/issues/347
Reviewed-on: https://gitea.com/gitea/runner/pulls/1348
Reviewed-by: bircni <[email protected]>

internal/pkg/config/config.example.yaml

@@ -327,8 +327,8 @@ health_check:
   # Minimum free space required on the filesystem holding runner workspaces.
   # Defaults to 1024 MiB when omitted or set to zero.
   #min_free_disk_space_mb: 1024
-  # Optional additional executable. A non-zero exit, timeout, or startup failure
-  # marks the runner unavailable.
+  # Optional additional executable, or a .bat or .cmd file on Windows. A non-zero
+  # exit, timeout, or startup failure marks the runner unavailable.
   #script: ''
   # How long a script result is cached and its maximum execution time.
   #interval: 30s