ref: upgrade unidiff to fix invalid escape SyntaxWarnings (#34650)

requirements-base.txt

@@ -65,7 +65,7 @@ symbolic==8.7.1
 toronado==0.1.0
 typing-extensions==3.10.0.2
 ua-parser==0.10.0
-unidiff==0.6.0
+unidiff==0.7.3
 urllib3[brotli]==1.25.11
 brotlipy==0.7.0
 # See if we can remove LDFLAGS from lib.sh