Update cryptography requirement from >=2.6,<39.0 to >=2.6,<40.0 (#878)

Updates the requirements on [cryptography](https://github.com/pyca/cryptography) to permit the latest version.
- [Release notes](https://github.com/pyca/cryptography/releases)
- [Changelog](https://github.com/pyca/cryptography/blob/main/CHANGELOG.rst)
- [Commits](pyca/cryptography@2.6...39.0.0)

---
updated-dependencies:
- dependency-name: cryptography
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
(cherry picked from commit 67809b4)

pyproject.toml

@@ -44,7 +44,7 @@ h2 = {version=">=4.1.0", optional=true, python=">=3.6.2"}
 requests-toolbelt = {version=">=0.9.1,<0.11.0", optional=true}
 requests = {version="^2.23.0", optional=true}
 idna = {version=">=2.1,<4.0", optional=true}
-cryptography = {version=">=2.6,<39.0", optional=true}
+cryptography = {version=">=2.6,<40.0", optional=true}
 trio = {version=">=0.14,<0.23", optional=true}
 curio = {version="^1.2", optional=true}
 sniffio = {version="^1.1", optional=true}