pre-commit: alter when 'nix build' runs

* do not run 'nix build' on arbitrary go src file changes, instead
  (except for nix and flake related changes) only run on module-wide
  changes, i.e. when sum,mod files change as these require flake
  vendorSha256 updates or else they would fail to build.

.pre-commit-config.yaml

@@ -66,6 +66,6 @@ repos:
         entry: nix build .#go-xkcdreader
         pass_filenames: false
         # trigger this hook on changes to any of nix (also flake.lock) files
-        # and go's src, mod or sum files
-        files: '\.*.(nix|lock|go|mod|sum)$'
+        # and go's mod or sum files
+        files: '\.*.(nix|lock|mod|sum)$'
         language: system