fix(shared): use constant POWERTOOLS_DEV env var

Co-authored-by: Leandro Damascena <[email protected]>

Author: heitorlessa

Diff for: aws_lambda_powertools/shared/functions.py

@@ -83,7 +83,7 @@ def bytes_to_string(value: bytes) -> str:
 
 
 def powertools_dev_is_set() -> bool:
-    is_on = strtobool(os.getenv("POWERTOOLS_DEV", "0"))
+    is_on = strtobool(os.getenv(constants.POWERTOOLS_DEV_ENV, "0"))
     if is_on:
         warnings.warn("POWERTOOLS_DEV environment variable is enabled. Increasing verbosity across utilities.")
         return True