chore: Fix docs-building and nightly-build in CI

[mrzimu]

This pull request includes updates to workflow configuration files and a minor documentation improvement in the C++ source code. The main changes focus on improving dependency installation, correcting scheduling, and enhancing naming consistency.

Workflow configuration improvements:

• Changed dependency installation in both .github/workflows/deploy-docs.yml and .github/workflows/test-package.yml to use editable mode (pip install -e .[docs]) to avoid autodoc error in CI documentation building. [1] [2]
• Updated the nightly build schedule in .github/workflows/nightly-build.yml to ensure it runs at the correct time (20:00 Beijing time).
• Renamed the workflow in .github/workflows/test-package.yml from "Run pytest" to "Test package" for improved clarity and consistency.

Code documentation improvement:

• Clarified wording in the C++ source file cpp/src/uproot-custom.cc regarding the reading of TObject from the buffer, making the documentation easier to read.