Move git command to git/gitcmd (#35483)

The name cmd is already used in many places and may cause conflicts, so
I chose `gitcmd` instead to minimize potential naming conflicts.

modules/git/utils.go

@@ -6,7 +6,6 @@ package git
 import (
 	"crypto/sha1"
 	"encoding/hex"
-	"fmt"
 	"io"
 	"strconv"
 	"strings"
@@ -42,14 +41,6 @@ func (oc *ObjectCache[T]) Get(id string) (T, bool) {
 	return obj, has
 }
 
-// ConcatenateError concatenats an error with stderr string
-func ConcatenateError(err error, stderr string) error {
-	if len(stderr) == 0 {
-		return err
-	}
-	return fmt.Errorf("%w - %s", err, stderr)
-}
-
 // ParseBool returns the boolean value represented by the string as per git's git_config_bool
 // true will be returned for the result if the string is empty, but valid will be false.
 // "true", "yes", "on" are all true, true