exclude plugin-tester-scala from Fossa scanning

[patriknw]

There are several build errors, such as:

Command execution failed: 
[132](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:133)
            command: Command {cmdName = "/home/runner/work/akka-grpc/akka-grpc/plugin-tester-java/gradlew", cmdArgs = ["projects"], cmdAllowErr = Never}
[133](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:134)
            dir: /home/runner/work/akka-grpc/akka-grpc/plugin-tester-java/
[134](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:135)
            exit: ExitFailure 1
[135](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:136)
            stdout: 
[136](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:137)
              
[137](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:138)
            stderr: 
[138](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:139)
              
[139](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:140)
              FAILURE: Build failed with an exception.
[140](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:141)

[141](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:142)
              * Where:
[142](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:143)
              Settings file '/home/runner/work/akka-grpc/akka-grpc/plugin-tester-java/settings.gradle' line: 12
[143](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:144)

[144](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:145)
              * What went wrong:
[145](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:146)
              A problem occurred evaluating settings 'plugin-tester-java'.
[146](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:147)
              > System property `akka.grpc.project.version` is not provided. Use -Dakka.grpc.project.version=$VERSION.
[147](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:148)

[148](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:149)
              * Try:
[149](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:150)
              Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
[150](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:151)

[151](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:152)
              * Get more help at https://help.gradle.org/
[152](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:153)

[153](https://github.com/akka/akka-grpc/actions/runs/3110670244/jobs/5042097600#step:5:154)
              BUILD FAILED in 1s