Integrate Scalar into the CI builds

During the review of the initial Scalar patch series, it was suggested to include Scalar in Git's CI builds. Due to some conflicts, this was postponed to a later patch series: This patch series.

Note that the changes to the GitHub workflow are somewhat transient in
nature: Based on the feedback I received on the Git mailing list, I see some appetite for turning Scalar into a full-fledged top-level command in Git, similar to gitk. Therefore my current plan is to do exactly that in the end (and I already have patches lined up to that end). This will essentially revert the ci/run-build-and-tests.sh change in this patch series.

This patch series is based on js/scalar-diagnose.

Johannes Schindelin (2):
cmake: optionally build scalar, too
ci: also run the scalar tests

 .github/workflows/main.yml          | 15 +++++++++++++++
 ci/run-build-and-tests.sh           |  2 ++
 ci/run-test-slice.sh                |  5 +++++
 contrib/buildsystems/CMakeLists.txt | 14 ++++++++++++++
 4 files changed, 36 insertions(+)

base-commit: 15d8adccab9a3146b760b089df59ce3e7ca2b451
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1129%2Fdscho%2Fscalar-and-ci-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1129/dscho/scalar-and-ci-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1129

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