execute_sql hangs forever until you call .rows on the results

#### Problem

When calling `execute_sql` the program hangs forever (I had to kill -9 it) unless you read from .rows.

#### Environment details

- OS: MacOS
- Ruby version: 3.4.2
- Gem name and version: google-cloud-spanner 2.26

#### Steps to reproduce

1. Create a client
2. `client.execute_sql`
3. Never read the result from `execute_sql`
4. Program hangs forever

#### Code example

```ruby
require "google/cloud/spanner"

puts "Starting"
emulator_host = ENV.fetch("SPANNER_EMULATOR_HOST", nil)
project_id = ENV.fetch("SPANNER_EMULATOR_PROJECT", "")
instance_id = ENV.fetch("SPANNER_EMULATOR_INSTANCE", "")
database_id = ENV.fetch("SPANNER_EMULATOR_DATABASE", "")

puts "Creating project"
project = Google::Cloud::Spanner.new(
project_id: project_id,
emulator_host: emulator_host,
)

puts "Creating client"
client = project.client(instance_id, database_id)

puts "Executing sql"
puts client.execute_sql("SELECT * FROM my_table")
```

Change the last line to:

`puts client.execute_sql("SELECT * FROM my_table").rows.first`

And it will no longer hang.

#### Full backtrace

There is no backtrace, the program just hangs forever after printing "Executing sql"