docs: brush up some python docs (#5027)

docs/src/auth.md

@@ -227,7 +227,7 @@ async def main():
         browser = await p.chromium.launch_persistent_context(userDataDir, headless=False)
         # Execute login steps manually in the browser window
 
-asyncio.get_event_loop().run_until_complete(main())
+asyncio.run(main())
 ```
 
 ```python sync

docs/src/ci.md

@@ -296,7 +296,7 @@ async def main():
          # Works across chromium, firefox and webkit
          browser = await p.chromium.launch(headless=False)
 
-asyncio.get_event_loop().run_until_complete(main())
+asyncio.run(main())
 ```
 
 ```python sync

docs/src/cli.md

@@ -17,8 +17,8 @@ $ npx playwright --help
 $ python -m playwright
 ```
 
-Running from `package.json` script
-```json
+```json js
+# Running from `package.json` script
 {
   "scripts": {
     "help": "playwright --help"

docs/src/core-concepts.md

@@ -38,7 +38,7 @@ async def main():
         browser = await p.chromium.launch(headless=False)
         await browser.close()
 
-asyncio.get_event_loop().run_until_complete(main())
+asyncio.run(main())
 ```
 
 ```python sync
@@ -113,7 +113,7 @@ async def main():
         page = await browser.newPage()
         await browser.close()
 
-asyncio.get_event_loop().run_until_complete(main())
+asyncio.run(main())
 ```
 
 ```python sync