FileConventions: account for .env prefix

When chceking versions in yaml files, correctly process case
when environment variable is referenced using `env.` prefix,
e.g. `env.FOO`.

src/FileConventions/Library.fs

@@ -337,9 +337,15 @@ let private DetectInconsistentVersionsInYamlFiles
                                     yamlDict.Children.["env"]
                                     :?> YamlMappingNode
 
-                                let envVarName =
+                                let referenceString =
                                     variableRegexMatch.Groups.[1].Value
 
+                                let envVarName =
+                                    if referenceString.StartsWith "env." then
+                                        referenceString.[4..]
+                                    else
+                                        referenceString
+
                                 match envDict.Children.TryGetValue envVarName
                                     with
                                 | true, envVarValue ->