Support protobuf==5 (#358)

We want to support protobuf==5 && protobuf==6 (and not restrict the
eventual jump to 7). We'll presumably drop support for 5 when 7 is
released, and re-lock our minimum at 6.

Resolves #356.

Author: stefanvanburen

.github/workflows/ci.yaml

@@ -19,6 +19,9 @@ jobs:
       matrix:
         python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
         resolution: ["highest", "lowest-direct"]
+    env:
+      # Shared env variables for all the tests
+      UV_RESOLUTION: '${{ matrix.resolution }}'
     steps:
       - name: Checkout code
         uses: actions/checkout@v5
@@ -32,8 +35,8 @@ jobs:
       - uses: astral-sh/setup-uv@v6
         with:
           python-version: ${{ matrix.python-version }}
-      - name: Install dependencies with resolution ${{ matrix.resolution }}
-        run: UV_RESOLUTION=${{ matrix.resolution }} make install
+      - name: Install dependencies
+        run: make install
       - name: Execute tests
         run: make test
       - name: Lint

buf.gen.yaml

@@ -2,8 +2,8 @@ version: v2
 managed:
   enabled: true
 plugins:
-    # NOTE: v30.0 is the earliest version supporting protobuf==6.
-    - remote: buf.build/protocolbuffers/python:v30.0
+    # NOTE: v26.0 is the earliest version supporting protobuf==5.
+    - remote: buf.build/protocolbuffers/python:v26.0
       out: gen
-    - remote: buf.build/protocolbuffers/pyi:v30.0
+    - remote: buf.build/protocolbuffers/pyi:v26.0
       out: gen