[STAL-3119] Fix folder structure for Windows release zip

[jasonforal]

What problem are you trying to solve?

With #534, we changed the action steps that performed the release, and in doing so, inadvertently changed the folder structure of the zip for Windows.

For example, it's now:

.
└── target
    └── x86_64-pc-windows-msvc
        └── release
            └── datadog-static-analyzer.exe

Whereas before, it was:

.
└── datadog-static-analyzer.exe

What is your solution?

Fix the invocation of 7z so it creates the archive with the exe at the root level.

You can see a successful run of this (and download the binaries and confirm a root level exe here: https://github.com/DataDog/datadog-static-analyzer/releases/tag/pre-release-110424-2)

Alternatives considered

What the reviewer should know

• d73cdbc triggered a pre-release to test this only for Windows. It will be force-pushed away before merging.