config.yml: Explicitly specify Debian stretch for previous Perls

Retain older Perls 5.20 through 5.24 under Debian stretch for less
suprises; people can copy and modify these over to Debian buster
manually if needed.

Author: zakame

config.yml

@@ -46,12 +46,15 @@ releases:
 
   - version: 5.20.3
     sha256:  1b40068166c242e34a536836286e70b78410602a80615143301e52aa2901493b
+    debian_release: stretch
 
   - version: 5.22.4
     sha256:  8b3122046d1186598082d0e6da53193b045e85e3505e7d37ee0bdd0bdb539b71
+    debian_release: stretch
 
   - version: 5.24.4
     sha256:  e34ff38c54857f431f37403b757267c9998152bf46b5c750b462f62461279b10
+    debian_release: stretch
 
   - version: 5.26.3
     sha256:  9ff35a613213f29ab53975141af6825ae7d4408895538cac0922e47ab92a1477