fix environment variable (#59)

Hello,

On Zed editor, when opening the file `Rust/.woodpecker.yaml`, it lints as danger (red) line 9:

031e75e884/Rust/.woodpecker.yaml (L9)

stating that:

```
yaml-schema: Woodpecker pipeline config: Incorrect type. Expected "step_environment".
```

But it can easily be fixed changing it to:

```diff
-   environment: [CARGO_TERM_COLOR=always]
+   environment:
+     CARGO_TERM_COLOR: always
```

as shown here:
https://woodpecker-ci.org/docs/usage/environment

Zed editor shows it is an error according to the schema in
https://raw.githubusercontent.com/woodpecker-ci/woodpecker/main/pipeline/frontend/yaml/linter/schema/schema.json

Reviewed-on: https://codeberg.org/Codeberg-CI/examples/pulls/59
Reviewed-by: 6543 <6543@obermui.de>
Co-authored-by: Simx72 <angel2600@proton.me>
Co-committed-by: Simx72 <angel2600@proton.me>

Rust/.woodpecker.yaml

@@ -6,7 +6,8 @@ steps:
     when:
       event: [push, pull_request]
     image: rust
-    environment: [CARGO_TERM_COLOR=always]
+    environment:
+      CARGO_TERM_COLOR: always
     commands:
       - rustup default $RUST
       - cargo check