ci: bump virtualenv from 20.26.2 to 20.26.3 in /.github/workflows (#697)

Bumps [virtualenv](https://github.com/pypa/virtualenv) from 20.26.2 to 20.26.3.
- [Release notes](https://github.com/pypa/virtualenv/releases)
- [Changelog](https://github.com/pypa/virtualenv/blob/main/docs/changelog.rst)
- [Commits](https://github.com/pypa/virtualenv/compare/20.26.2...20.26.3)

---
updated-dependencies:
- dependency-name: virtualenv
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/constraints.txt

@@ -2,5 +2,5 @@ pip==24.1
 nox==2024.4.15
 nox-poetry==1.0.3
 poetry==1.8.3
-virtualenv==20.26.2
+virtualenv==20.26.3
 toml==0.10.2