build: filter out .git folder for go generate check (#31265)

Fixes lint issue

    >>> /home/appveyor/.gvm/gos/go1.24.0/bin/go generate ./...
    ci.go:404: File changed: .git/index
    ci.go:407: One or more generated files were updated by running 'go generate ./...'
    exit status 1

Author: rjl493456442

build/ci.go

@@ -380,7 +380,7 @@ func doCheckGenerate() {
 	var hashes map[string][32]byte
 
 	var err error
-	hashes, err = build.HashFolder(".", []string{"tests/testdata", "build/cache"})
+	hashes, err = build.HashFolder(".", []string{"tests/testdata", "build/cache", ".git"})
 	if err != nil {
 		log.Fatal("Error computing hashes", "err", err)
 	}
@@ -395,7 +395,7 @@ func doCheckGenerate() {
 	build.MustRun(c)
 
 	// Check if generate file hashes have changed
-	generated, err := build.HashFolder(".", []string{"tests/testdata", "build/cache"})
+	generated, err := build.HashFolder(".", []string{"tests/testdata", "build/cache", ".git"})
 	if err != nil {
 		log.Fatalf("Error re-computing hashes: %v", err)
 	}