chore: use guess-next-dev instead of release-branch-semver [2.18] (#1…

…1723)

This PR updates the `version_schema` in the `../pyproject.toml` file for
the 2.18 release branch from `release-branch-semver` to
`guess-next-dev`. This is to ensure that system tests work as intended
with backports to this release branch.

IMPORTANT: This PR needs to be merged before the first backport is
created for 2.18.Otherwise, system tests will not work as expected.

- [x] Reviewer check

pyproject.toml

@@ -71,7 +71,7 @@ Homepage = "https://github.com/DataDog/dd-trace-py"
 "Source Code" = "https://github.com/DataDog/dd-trace-py/"
 
 [tool.setuptools_scm]
-version_scheme = "release-branch-semver"  # Must be "release-branch-semver" for now in main, see https://github.com/DataDog/dd-trace-py/issues/8801
+version_scheme = "guess-next-dev"  # Must be "release-branch-semver" for now in main, see https://github.com/DataDog/dd-trace-py/issues/8801
 write_to = "ddtrace/_version.py"
 
 [tool.cython-lint]