poetry, CI: insist in protobuf v21.12 in both Python and CI.

And re-ran poetry update which updated the lock file ofc.
Signed-off-by: Rusty Russell <[email protected]>

.github/scripts/setup.sh

@@ -73,10 +73,28 @@ curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- \
 
 # We also need a relatively recent protobuf-compiler, at least 3.12.0,
 # in order to support the experimental `optional` flag.
-PROTOC_VERSION=3.15.8
+
+# BUT WAIT!  Gentoo wants this to match the version from the Python protobuf,
+# which comes from the same tree.  Makes sense!
+
+# And
+#   grpcio-tools-1.54.0` requires `protobuf = ">=4.21.6,<5.0dev"`
+
+# Now, protoc changed to date-based releases, BUT Python protobuf
+# didn't, so Python protobuf 4.21.12 (in Ubuntu 23.04) corresponds to
+# protoc 21.12 (which, FYI, is packaged in Ubuntu as version 3.21.12).
+
+# So we're going to nail these versions as 21.12, which is what recent
+# Ubuntu has, and hopefully everyone else can get.  And this means that
+# When CI checks that no files have changed under regeneration, you won't
+# get a fail just because the dev's protoc is a different version.
+
+# Honorable mention go to Matt Whitlock for spelunking this horror with me!
+
+PROTOC_VERSION=21.12
 PB_REL="https://github.com/protocolbuffers/protobuf/releases"
 curl -LO $PB_REL/download/v${PROTOC_VERSION}/protoc-${PROTOC_VERSION}-linux-x86_64.zip
-sudo unzip protoc-3.15.8-linux-x86_64.zip -d /usr/local/
+sudo unzip protoc-${PROTOC_VERSION}-linux-x86_64.zip -d /usr/local/
 sudo chmod a+x /usr/local/bin/protoc
 export PROTOC=/usr/local/bin/protoc
 export PATH=$PATH:/usr/local/bin