Bump to Release-1.1.18

[eunos-1128]

This pull request updates the io.github.pemsley.coot.yaml file to improve module configurations and dependencies. The most important changes involve updating build options and source references for better compatibility and stability.

Module Configuration Updates:

• Updated the gemmi module's config-opts to use -DUSE_PYTHON=ON instead of -DUSE_PYTHON=1 for consistency with CMake conventions.
• Changed the gemmi module's source tag from v0.7.1 to v0.7.3 to use the latest available version.

Dependency Updates:

• Updated the coot module's source reference from a specific commit (a374e0364bbe7b9eb06b5c8302db38d24ae02007) to a tagged release (Release-1.1.18) for better versioning and clarity.

[flathubbot]

🚧 Test build enqueued.

[flathubbot]

🚧 Started test build.

[flathubbot]

✅ Test build succeeded. To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/201647/io.github.pemsley.coot.flatpakref