Sync Go version from go.mod

[davosian]

This pull request updates the project to use Go version 1.26.0 and ensures that the Go version is consistently sourced from go.mod across all build environments. The changes improve maintainability by eliminating hardcoded Go versions and aligning Docker, CI, and Nix builds with the version specified in go.mod.

Go version management improvements:

• Updated go.mod to specify Go version 1.26.0, replacing the previous 1.25 version.
• Modified both Dockerfile and Dockerfile.test to use a build argument GO_VERSION, which defaults to 1.26.0 and is now dynamically set instead of hardcoded. [1] [2]
• Updated docker-compose.test.yml to pass the GO_VERSION build argument from the environment, ensuring test containers use the correct Go version.

CI/CD workflow enhancements:

• Changed .github/workflows/ci.yaml to extract the Go version from go.mod and set it as an environment variable for build steps, ensuring CI uses the correct Go version. [1] [2] [3]

Nix build improvements:

• Updated default.nix to read the Go version from go.mod and select the appropriate Go package from nixpkgs, eliminating manual version updates.

[github-actions]

✅ Docker images built successfully for all platforms!

CI run: https://github.com/ajilach/clamav-rest/actions/runs/22859325418

[arizon-dread]

Great contribution!