azure-pipelines: fix target branch

As the variable name states, the target branch should contain
information about the branch against which the new commits / pull
request are redirected. Currently the variable contains the name of the
branch on which the commits are made (source branch). Update the
variable value accordingly.

Signed-off-by: Antoniu Miclaus <[email protected]>

Author: amiclaus

azure-pipelines.yml

@@ -10,7 +10,7 @@ pr:
 
 variables:
   runCondition: true
-  targetBranch: $[ variables['Build.SourceBranchName'] ]
+  targetBranch: $[ variables['System.PullRequest.TargetBranchName'] ]
 
 jobs:
 - job: LinuxBuilds