Make sure $pgConfig is not empty

For this workflow, using the runner-supplied PG, it can just be
pg_config and rely on the PATH. Which would be the default if it
were not supplied, but more of the script would have to be touched
to remove uses of the variable than just to set it to pg_config.

Author: jcflack

.github/workflows/ci-runnerpg.yml

@@ -55,6 +55,8 @@ jobs:
     - name: Install and test PL/Java
       working-directory: pljava
       run: |
+        pgConfig=pg_config # runner-supplied, just get it from the PATH
+
         packageJar=$(find pljava-packaging -name pljava-pg*.jar -print)
 
         mavenRepo="$HOME/.m2/repository"