Require explicit opt-in for GitHub and Gitlab formats

Author: charliermarsh

README.md

@@ -1327,8 +1327,9 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install ruff
+      # Include `--format=github` to enable automatic inline annotations.
       - name: Run Ruff
-        run: ruff .
+        run: ruff --format=github .
 ```
 
 ## FAQ

src/settings/types.rs

@@ -164,17 +164,6 @@ pub enum SerializationFormat {
 
 impl Default for SerializationFormat {
     fn default() -> Self {
-        if let Ok(github_actions) = env::var("GITHUB_ACTIONS") {
-            if github_actions == "true" {
-                return Self::Github;
-            }
-        }
-
-        if let Ok(gitlab_ci) = env::var("GITLAB_CI") {
-            if gitlab_ci == "true" {
-                return Self::Gitlab;
-            }
-        }
         Self::Text
     }
 }