I have a pipeline job set up as such:

• "This build is parameterized" with a "PRODUCT_CONFIG_BRANCH" string parameter
• "Pipeline script from SCM" with branch specifier `refs/heads/$PRODUCT_CONFIG_BRANCH`
  When I run the build, it never seems to read the $PRODUCT_CONFIG_BRANCH variable.

If I set the variable in the Properties Content section, it uses this. However, I'd prefer to be able to easily set it every time I click Build.