README.md: astral-sh/ruff-action@v1 --> v2 (#21)

README.md upgraded to match
https://github.com/astral-sh/ruff-action/releases
```diff
- - uses: astral-sh/ruff-action@v1
+ - uses: astral-sh/ruff-action@v2
```

README.md

@@ -42,15 +42,15 @@ fix).
 ### Specify a different source directory
 
 ```yaml
-- uses: astral-sh/ruff-action@v1
+- uses: astral-sh/ruff-action@v2
   with:
     src: "./src"
 ```
 
 ### Specify multiple files
 
 ```yaml
-- uses: astral-sh/ruff-action@v1
+- uses: astral-sh/ruff-action@v2
   with:
     src: >-
       path/to/file1.py
@@ -62,15 +62,15 @@ fix).
 This action adds ruff to the PATH, so you can use it in subsequent steps.
 
 ```yaml
-- uses: astral-sh/ruff-action@v1
+- uses: astral-sh/ruff-action@v2
 - run: ruff check --fix
 - run: ruff format
 ```
 
 ### Use `ruff format`
 
 ```yaml
-- uses: astral-sh/ruff-action@v1
+- uses: astral-sh/ruff-action@v2
   with:
     args: "format --check"
 ```