Fix support for Windows Batch

Test builds:

• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-linux-386
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-linux-amd64
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-linux-arm
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-darwin-386
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-darwin-amd64
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-windows-386.exe
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-windows-amd64.exe
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-freebsd-386
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-freebsd-amd64
• https://gitlab-ci-multi-runner-downloads.s3.amazonaws.com/fix-cmd-shell/binaries/gitlab-ci-multi-runner-freebsd-arm

Fixes https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1052