Update networkx requirement from >=2.6 to >=3.4.2

Updates the requirements on [networkx](https://github.com/networkx/networkx) to permit the latest version.
- [Release notes](https://github.com/networkx/networkx/releases)
- [Commits](networkx/networkx@networkx-2.6...networkx-3.4.2)

---
updated-dependencies:
- dependency-name: networkx
  dependency-version: 3.4.2
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -2,5 +2,5 @@ prov == 1.5.3
 bdbag >= 1.4.1
 arcp >= 0.2.0
 rdflib >= 6, <8
-networkx>=2.6;python_version>"3.6"  # not directly required, pinned by Snyk to avoid a vulnerability
+networkx>=3.4.2;python_version>"3.6"  # not directly required, pinned by Snyk to avoid a vulnerability
 typing_extensions