reduce visual noise

Author: tshepang

src/conventions.md

@@ -34,7 +34,7 @@ don't have a stable C API.
 When modifying that code, use this command to format it:
 
 ```console
-./x test tidy --extra-checks=cpp:fmt --bless
+./x test tidy --extra-checks cpp:fmt --bless
 ```
 
 This uses a pinned version of `clang-format`, to avoid relying on the local
@@ -47,12 +47,12 @@ it both linted and formatted by the [ruff][ruff] tool.
 
 When modifying Python code, use this command to format it:
 ```console
-./x test tidy --extra-checks=py:fmt --bless
+./x test tidy --extra-checks py:fmt --bless
 ```
 
 and the following command to run lints:
 ```console
-./x test tidy --extra-checks=py:lint
+./x test tidy --extra-checks py:lint
 ```
 
 This uses a pinned version of `ruff`, to avoid relying on the local