PEP 704: Drop a redundant word

Co-authored-by: Jelle Zijlstra <[email protected]>

Author: pradyunsg

pep-0704.rst

@@ -50,7 +50,7 @@ Installers MAY choose to implement this default behaviour on any Python versions
 Backwards Compatibility
 =======================
 
-This PEP is backwards incompatible with workflows where users who are using installers outside of virtual environments. Such users will be prompted with an error message and will need to either:
+This PEP is backwards incompatible with workflows where users are using installers outside of virtual environments. Such users will be prompted with an error message and will need to either:
 
 - explicitly opt-in to running the installer outside of a virtual environment, or
 - create and use a virtual environment