This updates smmap's CI configuration in ways that are in line with
recent updates to gitdb's. In most cases there is no difference in
the changes, and the reason for the updates is more to avoid
confusing differences than from the value of the changes
themselves. In one case, there is a major difference (fetch-depth).

- gitpython-developers/gitdb#89 (same)

- gitpython-developers/gitdb#90 (same)
  It's just the project, not dependencies, but otherwise the same.

- gitpython-developers/gitdb#92 (opposite)
  This is the major difference. We don't need more than the tip of
  the branch in these tests. Keeping the default fetch-depth of 1
  by not setting it explicitly avoids giving the impression that
  the tests here are doing something they are not (and also serves
  as a speed optimization).

- gitpython-developers/gitdb#93 (same)

Update CI, in line with gitdb

+ Make YAML indentation more consistent.

Since Python 3.12.0 stable has been released and is available via
setup-python, per:
https://github.com/actions/python-versions/blob/main/versions-manifest.json

This makes it so continue-on-error and allow-prereleases are no
longer special-cased to true for 3.12; instead, 3.12 is treaed the
same as other Python releases (where those are false).

No longer treat 3.12 as experimental on smmap CI

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 4 to 5.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v4...v5)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

…tions/actions/setup-python-5

Bump actions/setup-python from 4 to 5

This uses NamedTemporaryFile with delete=False to replace the one
use of the deprecated mktemp function in smmap (reported in #41).

This avoids the race condition inherent to mktemp, as the file is
named and created together in a way that is effectively atomic.

Because NamedTemporaryFile is not being used to automatically
delete the file, it use and cleanup are unaffected by the change.

Replace use of mktemp