DEV: Remove git_version from DiscourseLogstashLogger log event (#27730)

In our official Docker image, running git commands results in the
following error:

```
fatal: detected dubious ownership in repository at '/var/www/discourse'
To add an exception for this directory, call:

	git config --global --add safe.directory /var/www/discourse
```

spec/lib/discourse_logstash_logger_spec.rb

@@ -21,7 +21,6 @@ RSpec.describe DiscourseLogstashLogger do
           "pid" => described_class::PROCESS_PID,
           "type" => "test",
           "host" => described_class::HOST,
-          "git_version" => described_class::GIT_VERSION,
           "method" => "GET",
           "path" => "/",
           "format" => "html",