scripts/requirements: Replace protobuf with grpcio-tools

The nanopb module generates source files from .proto files,
however the latest protobuf v4.21.0 python package breaks
compatibility.
Using grpcio-tools instead fixes this.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>
diff --git a/scripts/requirements-extras.txt b/scripts/requirements-extras.txt
index bea2751..62bb2b9 100644
--- a/scripts/requirements-extras.txt
+++ b/scripts/requirements-extras.txt
@@ -22,7 +22,7 @@
 imgtool>=1.7.1
 
 # used by nanopb module to generate sources from .proto files
-protobuf
+grpcio-tools
 
 # used by scripts/release/bug_bash.py for generating top ten bug squashers
 PyGithub