Allow matching prefix with curly braces in CodeExample.prefix_settings() (#44)

The SuperFences markdown extensions uses the following format for attributes:
`lang-name {.extra-class attr="a"}`

See: https://facelessuser.github.io/pymdown-extensions/extensions/superfences/#injecting-classes-ids-and-attributes

Author: Viicos

pytest_examples/find_examples.py

@@ -76,7 +76,7 @@ def prefix_settings(self) -> dict[str, str]:
         This works on the format `py foo="bar" spam="with space"`.
         """
         settings = {}
-        for m in re.finditer(r'(\S+?)=([\'"])(.+?)\2', self.prefix):
+        for m in re.finditer(r'([^{\s]+?)=([\'"])(.+?)\2', self.prefix):
             settings[m.group(1)] = m.group(3)
         return settings