fix typo when assigning build_version in azure pipeline (#2044)

azure-pipelines.yml

@@ -58,7 +58,7 @@ stages:
             displayName: "Sign Crowdsec binaries + plugins"
 
           - pwsh: |
-              $build_version=$(Build.SourceBranchName)
+              $build_version=$Build.SourceBranchName
               if ($build_version.Contains("-")) 
               {
                 $build_version = $build_version.Substring(0, $build_version.IndexOf("-"))
@@ -69,7 +69,7 @@ stages:
             name: BuildMSI
 
           - pwsh: |
-              $build_version=$(Build.SourceBranchName)
+              $build_version=$Build.SourceBranchName
               if ($build_version.Contains("-")) 
               {
                 $build_version = $build_version.Substring(0, $build_version.IndexOf("-"))