Document GITEA_* env aliases, missing variables and accurate examples (#618)

https://gitea.com/gitea/runner/pulls/1358 mirrors every built-in `GITHUB_*` variable as `GITEA_*`. The variables page now lists both names for each, in the same paired style as the context table.

It also adds variables that runners already set but the page left out (`*_ACTOR_ID`, `*_REF_PROTECTED`, `*_REPOSITORY_ID`, `*_REPOSITORY_OWNER_ID`, `*_TRIGGERING_ACTOR`, `*_WORKFLOW_SHA`, `ACT`, `ImageOS`, `RUNNER_DEBUG`, `RUNNER_ENVIRONMENT`, `RUNNER_NAME`, `RUNNER_WORKSPACE`, `TRACEPARENT`, `TRACESTATE`).

Examples copied from GitHub's runner (`/home/runner/work/_temp/...` paths, `__run`, `ghs_***`) are replaced with the values gitea-runner and Gitea actually produce, using placeholder users, repositories and instance URLs.

The zh-cn and zh-tw pages get the environment variable section they never had.

Reviewed-on: https://gitea.com/gitea/docs/pulls/618
Reviewed-by: Lunny Xiao <[email protected]>
Co-authored-by: silverwind <[email protected]>

runner-docs/hooks/job-hooks.md

@@ -31,7 +31,7 @@ The shell options of `run:` steps do not apply to hooks. Set `pipefail` and othe
 
 ## Environment and output
 
-A hook receives the job's environment, including `runner.envs`, the workflow's `env:` and the `GITHUB_*` variables. The runner includes hook output in the job log and masks secrets as it does for step output.
+A hook receives the job's environment, including `runner.envs`, the workflow's `env:` and the `GITHUB_*` and `GITEA_*` variables. The runner includes hook output in the job log and masks secrets as it does for step output.
 
 Use `$GITHUB_ENV` and `$GITHUB_PATH` to pass environment variables and paths to later steps. Mask values with `::add-mask::`: