Strip CR from Git for Windows checksums in update-checksums.sh

What does this MR do?

Fixes the build failures seen on Renovate Git for Windows bumps such as !155 (merged).

The GitHub release body used to derive the Git for Windows checksums uses CRLF line endings. awk '{print $NF}' preserves the trailing carriage return, and bash command substitution strips a trailing \n but not \r, so the CR ends up embedded in the GIT_CHECKSUM value written into dockerfiles/runner-helper/docker-bake.hcl.

HCL then treats the embedded \r as a line break, and every docker buildx bake job fails with:

docker-bake.hcl:163: Invalid multi-line string;
Quoted strings may not be split over multiple lines.

Fix

Strip carriage returns from the release body (| tr -d '\r') when extracting the checksums, so the values are written on a single line.

Verified by re-running GIT_FOR_WINDOWS_TAG=v2.55.0.windows.3 ./scripts/update-checksums.sh locally: the resulting GIT_CHECKSUM line is a single clean line with no trailing CR.

Once this is merged, rebasing !155 (merged) will regenerate a valid docker-bake.hcl.

🤖 Generated with Claude Code