docs: Update RFS version & move "v" prefix to config.yml (#34918)

config.yml

@@ -50,7 +50,7 @@ params:
   current_version:      "5.1.1"
   current_ruby_version: "5.1.1"
   docs_version:         "5.1"
-  rfs_version:          "9.0.3"
+  rfs_version:          "v9.0.6"
   github_org:           "https://github.com/twbs"
   repo:                 "https://github.com/twbs/bootstrap"
   twitter:              "getbootstrap"

site/content/docs/5.1/getting-started/rfs.md

@@ -8,13 +8,13 @@ toc: true
 
 ## What is RFS?
 
-Bootstrap's side project [RFS](https://github.com/twbs/rfs/tree/v{{< param "rfs_version" >}}) is a unit resizing engine which was initially developed to resize font sizes (hence its abbreviation for Responsive Font Sizes). Nowadays RFS is capable of rescaling most CSS properties with unit values like `margin`, `padding`, `border-radius`, or even `box-shadow`.
+Bootstrap's side project [RFS](https://github.com/twbs/rfs/tree/{{< param "rfs_version" >}}) is a unit resizing engine which was initially developed to resize font sizes (hence its abbreviation for Responsive Font Sizes). Nowadays RFS is capable of rescaling most CSS properties with unit values like `margin`, `padding`, `border-radius`, or even `box-shadow`.
 
 The mechanism automatically calculates the appropriate values based on the dimensions of the browser viewport. It will be compiled into `calc()` functions with a mix of `rem` and viewport units to enable the responsive scaling behavior.
 
 ## Using RFS
 
-The mixins are included in Bootstrap and are available once you include Bootstrap's `scss`. RFS can also be [installed standalone](https://github.com/twbs/rfs/tree/v{{< param "rfs_version" >}}#installation) if needed.
+The mixins are included in Bootstrap and are available once you include Bootstrap's `scss`. RFS can also be [installed standalone](https://github.com/twbs/rfs/tree/{{< param "rfs_version" >}}#installation) if needed.
 
 ### Using the mixins
 
@@ -83,4 +83,4 @@ In this example, we use one of Bootstrap's built-in [responsive breakpoint mixin
 
 ## Extended documentation
 
-RFS is a separate project under the Bootstrap organization. More about RFS and its configuration can be found on its [GitHub repository](https://github.com/twbs/rfs/tree/v{{< param "rfs_version" >}}).
+RFS is a separate project under the Bootstrap organization. More about RFS and its configuration can be found on its [GitHub repository](https://github.com/twbs/rfs/tree/{{< param "rfs_version" >}}).