devtools/cmd/csphash: check for template expansion in scripts
devtools/cmd/csphash: check for template expansion in scripts

Report any scripts that will change dynamically due to a template
expansion. CSP hashing can't support scripts like that, because the
contents and therefore the hash will change on each execution.

Change-Id: I975859a59c8f5d19bcd0ffc5dad1e5068a380587
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/240500
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite