Prepare release 0.4.0

[avdv]

A new release is in order since version 0.3.0 that is currently published to the BCR is not compatible with Bazel 7, as it is failing on amd64 Darwin with:

(07:18:17) INFO: ToolchainResolution: Performing resolution of @@rules_sh~0.3.0//sh/posix:toolchain_type for target platform @@local_config_platform//:host
      ToolchainResolution:   Toolchain @@rules_sh~0.3.0~sh_configure~local_posix_config//:local_posix is compatible with target plaform, searching for execution platforms:
      ToolchainResolution:     Incompatible execution platform @@local_config_platform//:host; mismatching values: linux
      ToolchainResolution: No @@rules_sh~0.3.0//sh/posix:toolchain_type toolchain found for target platform @@local_config_platform//:host.
(07:18:17) INFO: ToolchainResolution: Performing resolution of @@rules_sh~0.3.0//sh/posix:toolchain_type for target platform @@local_config_platform//:host
      ToolchainResolution:   Toolchain @@rules_sh~0.3.0~sh_configure~local_posix_config//:local_posix is compatible with target plaform, searching for execution platforms:
      ToolchainResolution:     Incompatible execution platform @@local_config_platform//:host; mismatching values: linux
      ToolchainResolution: No @@rules_sh~0.3.0//sh/posix:toolchain_type toolchain found for target platform @@local_config_platform//:host.

This is caused by an unexpected os value, which is gets mapped to linux.

[aherrmann]

Looks good, thank you!