feat: gate set-env/add-path and render annotation locations (#1109)

`::set-env::` and `::add-path::` let a step rewrite the environment of every later step from its own output, which the runner honoured silently. They are now refused, as GitHub has done since 2020, and `ACTIONS_ALLOW_UNSECURE_COMMANDS` opts back in per step or job. Support for that variable is new here too, and is the only opt-in, matching GitHub rather than adding a runner config key on top.

Annotations keep their source location: Gitea has no annotation store and its web UI strips command properties, so `::error file=main.go,line=12::msg` is rendered as `::error::main.go:12: msg`.

`DEVELOPMENT.md` writes down the log line encoding rules this relies on.

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1109
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: bircni <bircni@icloud.com>

act/runner/testdata/GITHUB_ENV-use-in-env-ctx/push.yml

@@ -3,6 +3,7 @@ jobs:
   _:
     runs-on: ubuntu-latest
     env:
+      ACTIONS_ALLOW_UNSECURE_COMMANDS: 'true'
       MYGLOBALENV3: myglobalval3
     steps:
     - uses: actions/checkout@v4

act/runner/testdata/commands/push.yml

@@ -4,6 +4,8 @@ on: push
 jobs:
   build:
     runs-on: ubuntu-latest
+    env:
+      ACTIONS_ALLOW_UNSECURE_COMMANDS: 'true'
     steps:
       - name: TEST set-env
         run: echo "::set-env name=foo::bar"