Fix typos (#37346)

Fixes some typos

routers/api/v1/user/avatar.go

@@ -13,7 +13,7 @@ import (
 	user_service "code.gitea.io/gitea/services/user"
 )
 
-// UpdateAvatar updates the Avatar of an User
+// UpdateAvatar updates the Avatar of a User
 func UpdateAvatar(ctx *context.APIContext) {
 	// swagger:operation POST /user/avatar user userUpdateAvatar
 	// ---
@@ -45,7 +45,7 @@ func UpdateAvatar(ctx *context.APIContext) {
 	ctx.Status(http.StatusNoContent)
 }
 
-// DeleteAvatar deletes the Avatar of an User
+// DeleteAvatar deletes the Avatar of a User
 func DeleteAvatar(ctx *context.APIContext) {
 	// swagger:operation DELETE /user/avatar user userDeleteAvatar
 	// ---