reproducible builds: pekko-grpc-sbt-plugin pom extraDependencyAttributes

Checking for reproducible builds, we found a difference in the pom for pekko-grpc-sbt-plugin, notably in the `extraDependencyAttributes` property

```
+organisation:#@#:+com.thesamet:#@#:+branch:#@#:+@#:NULL:#@:#@#:+e:sbtVersion:#@#:+1.0:#@#:+module:#@#:+sbt-protoc_2.12_1.0:#@#:+revision:#@#:+1.1.0-RC2:#@#:+e:scalaVersion:#@#:+2.12:#@#:
+organisation:#@#:+com.github.sbt:#@#:+branch:#@#:+@#:NULL:#@:#@#:+e:sbtVersion:#@#:+1.0:#@#:+module:#@#:+sbt2-compat_2.12_1.0:#@#:+revision:#@#:+0.1.0:#@#:+e:scalaVersion:#@#:+2.12:#@#:
```
vs
```
+e:sbtVersion:#@#:+1.0:#@#:+module:#@#:+sbt-protoc_2.12_1.0:#@#:+e:scalaVersion:#@#:+2.12:#@#:+organisation:#@#:+com.thesamet:#@#:+branch:#@#:+@#:NULL:#@:#@#:+revision:#@#:+1.1.0-RC2:#@#:
+e:sbtVersion:#@#:+1.0:#@#:+module:#@#:+sbt2-compat_2.12_1.0:#@#:+e:scalaVersion:#@#:+2.12:#@#:+organisation:#@#:+com.github.sbt:#@#:+branch:#@#:+@#:NULL:#@:#@#:+revision:#@#:+0.1.0:#@#:
```

This attribute is added by sbt, and it seems the ordering is not stable. We should further diagnose this and ideally fix it upstream in sbt, otherwise in post-processing.