ci(sheets): exempt internal/gen generators from forbidigo

The shortcuts/sheets/internal/gen code generator is a standalone
`package main` run via go:generate, not shortcut runtime code, so the
forbidigo bans on log.Fatal / os.ReadFile / fmt.Printf do not apply.
Making it "compliant" is impossible anyway: a structured error return
needs os.Exit (also banned), and the vfs alternative is blocked by
depguard shortcuts-no-vfs. Exempt shortcut internal/gen paths, matching
the existing _test.go and internal/vfs forbidigo exemptions.

.golangci.yml

@@ -57,6 +57,14 @@ linters:
       - path: internal/vfs/
         linters:
           - forbidigo
+      # internal/gen build-time generators (standalone `package main` run via
+      # go:generate) are not shortcut runtime code — no ctx/runtime/framework —
+      # so the shortcut forbidigo bans don't apply. Going "compliant" is also
+      # impossible here: a structured error return needs os.Exit (also banned),
+      # and the vfs.Xxx() alternative is blocked by depguard shortcuts-no-vfs.
+      - path: shortcuts/.*/internal/gen/
+        linters:
+          - forbidigo
       # shortcuts-no-raw-http is shortcuts-only; internal/ wraps raw HTTP
       # for the client / credential layer.
       - path-except: shortcuts/