v0.3.4.1

Changes since v0.3.4:

• No functional changes to the library code.
• Apply some GitHub Actions workflow adjustments as recommended by zizmor.
• Migrate the build-system dependency for the package from poetry to poetry-core.
• Update a few poetry lockfile dependencies (notably, explicitly confirming availability using urllib3 v2.x onwards, although in practice I believe this was already the case).