Use Protobuf v25.5 in test_scala_version

As mentioned in the comments, Protobuf v25.5 is the maximum version
supported by ScalaPB 0.9.8 (for Scala 2.11) and 0.11.17.

This change sets up a future change to conditionally set Protobuf to
v25.5 when testing Scala 2.11 after other Scala version update to
ScalaPB 1.0.0-alpha.1. The test will use Protobuf v28.3 with those other
Scala versions.

Protobuf versions v26.x and v27.x aren't supported by any ScalaPB
version.

The `RULES_SCALA_TEST_ONLY` environment variable was invaluable for
determining these parameters, as it allowed quickly trying versions with
commands like:

```txt
$ RULES_SCALA_TEST_ONLY='test_scala_version 2.11.12' ./test_version.sh
```

Author: mbland

test_version.sh

@@ -49,7 +49,17 @@ run_in_test_repo() {
     scrooge_ws="scrooge_repositories($version_param)"
   fi
 
+  # ScalaPB 0.9.8 through 0.11.17 can support at least Protobuf v21.7 up to
+  # Protobuf v25.5. ScalaPB 1.0.0-alpha.1 requires at least Protofuf 28.2.
+  # Protobuf versions v26.x and v27.x aren't supported by any ScalaPB version.
+  local protobuf_version='25.5'
+  local protobuf_sha=(
+    '3cf7d5b17c4ff04fe9f038104e9d0cae6da09b8ce271c13e44f8ac69f51e4e0f'
+  )
+
   sed -e "s%\${twitter_scrooge_repositories}%${scrooge_ws}\n%" \
+      -e "s%\${protobuf_version}%${protobuf_version}%g" \
+      -e "s%\${protobuf_sha}%${protobuf_sha}%g" \
       WORKSPACE.template >> $NEW_TEST_DIR/WORKSPACE
   cp ../.bazel{rc,version} $NEW_TEST_DIR/
 

test_version/WORKSPACE.template

@@ -31,9 +31,9 @@ http_archive(
 
 http_archive(
     name = "com_google_protobuf",
-    sha256 = "75be42bd736f4df6d702a0e4e4d30de9ee40eac024c4b845d17ae4cc831fe4ae",
-    strip_prefix = "protobuf-21.7",
-    url = "https://github.com/protocolbuffers/protobuf/archive/refs/tags/v21.7.tar.gz",
+    sha256 = "${protobuf_sha}",
+    strip_prefix = "protobuf-${protobuf_version}",
+    url = "https://github.com/protocolbuffers/protobuf/archive/refs/tags/v${protobuf_version}.tar.gz",
 )
 
 load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies")