[release-2.9.x] docs: master tag hasn't been pushed for almost 2 years (#10635)

Backport f184c5db51 from #10633

Co-authored-by: Šimon Lukašík <isimluk@fedoraproject.org>

docs/sources/send-data/fluentd/_index.md

@@ -26,7 +26,7 @@ fluent-gem install fluent-plugin-grafana-loki
 
 ## Docker Image
 
-The Docker image `grafana/fluent-plugin-loki:master` contains [default configuration files](https://github.com/grafana/loki/tree/main/clients/cmd/fluentd/docker/conf). By default, fluentd containers use that default configuration. You can instead specify your `fluentd.conf` configuration file with a `FLUENTD_CONF` environment variable.
+The Docker image `grafana/fluent-plugin-loki:main` contains [default configuration files](https://github.com/grafana/loki/tree/main/clients/cmd/fluentd/docker/conf). By default, fluentd containers use that default configuration. You can instead specify your `fluentd.conf` configuration file with a `FLUENTD_CONF` environment variable.
 
 This image also uses `LOKI_URL`, `LOKI_USERNAME`, and `LOKI_PASSWORD` environment variables to specify the Loki's endpoint, user, and password (you can leave the USERNAME and PASSWORD blank if they're not used).
 
@@ -39,7 +39,7 @@ A Docker Compose configuration that will work looks like:
 ```yaml
 services:
   fluentd:
-    image: grafana/fluent-plugin-loki:master
+    image: grafana/fluent-plugin-loki:main
     command:
       - "fluentd"
       - "-v"