Update context and function descriptions

[muzimuzhi]

• Add descriptions for newly added github context properties (see #57), with version constraints "ghes >= 3.9 or ghae >= 3.9"
• Update existing descriptions
• Drop deprecated version constraints "ghes > 3.3 or ghae > 3.3" and "ghes > 3.4 or ghae > 3.5"

Note:

• Existing version constraint used "ghes": "3.3" to represent "strict larger than" relation ghes > 3.3. Here I use "ghes": ">=3.9" to represent "equal to or larger than" relation. (It seems currently the versions key is not used so there exists the space/chance to extend its schema.)

Useful links

• GitHub Actions Contexts https://docs.github.com/en/actions/learn-github-actions/contexts and its source in github/docs repo
• GitHub Actions Expressions https://docs.github.com/en/actions/learn-github-actions/expressions
• Commits that deprecated 3.3 and 3.5 version constraints https://github.com/github/docs/commit/ac2cd0e47de1c4c4ea654c9fd36b7a9ff9ea5a50, https://github.com/github/docs/commit/fefcf3b5a60aea2443b6392dcd56e367f55a1ceb, and https://github.com/github/docs/commit/19ded728c0fc06dc2a4d939ac7026fc050671ebc
• Commit that adds 3.9 version constraints https://github.com/github/docs/commit/83bdd63b1d133783004b22c9330c2b6179c98818