Pipeline proto seems to be incorrect for Combine.GroupedValues

It looks like CombineTest$BasicTests#testHotKeyCombining on Dataflow (and possibly other runners) is creating an invalid pipeline proto since the transform doesn't an environment (and possible a spec):
```

I0610 16:05:23.791430 14054 fnapi_instruction_graph_rewriter.cc:230] transforms {
I0610 16:05:23.791402
14054 fnapi_instruction_graph_rewriter.cc:230] key: "HotMean/PostCombine/Combine.GroupedValues"
I0610
16:05:23.791404 14054 fnapi_instruction_graph_rewriter.cc:230] value {
I0610 16:05:23.791406
14054 fnapi_instruction_graph_rewriter.cc:230] inputs {
I0610 16:05:23.791408 14054 fnapi_instruction_graph_rewriter.cc:230]
key: "org.apache.beam.sdk.values.PCollection.:400#56b99bb29b40d50c"
I0610 16:05:23.791410
14054 fnapi_instruction_graph_rewriter.cc:230] value: "HotMean/PostCombine/GroupByKey.out"
I0610
16:05:23.791412 14054 fnapi_instruction_graph_rewriter.cc:230] }
I0610 16:05:23.791414 14054
fnapi_instruction_graph_rewriter.cc:230] outputs {
I0610 16:05:23.791416 14054 fnapi_instruction_graph_rewriter.cc:230]
key: "org.apache.beam.sdk.values.PCollection.:400#4fa4d31096ca160c"
I0610 16:05:23.791419
14054 fnapi_instruction_graph_rewriter.cc:230] value: "HotMean/PostCombine/Combine.GroupedValues/ParDo(Anonymous)/ParMultiDo(Anonymous).output"
I0610
16:05:23.791421 14054 fnapi_instruction_graph_rewriter.cc:230] }
I0610 16:05:23.791423 14054
fnapi_instruction_graph_rewriter.cc:230] unique_name: "HotMean/PostCombine/Combine.GroupedValues"
I0610
16:05:23.791426 14054 fnapi_instruction_graph_rewriter.cc:230] }
I0610 16:05:23.791428 14054
fnapi_instruction_graph_rewriter.cc:230] }
```

Imported from Jira [BEAM-10266](https://issues.apache.org/jira/browse/BEAM-10266). Original Jira may contain additional context.
Reported by: lcwik.
Subtask of issue #18583

Start with CombineTest$BasicTests#testHotKeyCombining and inspect the generated pipeline proto for Combine.GroupedValues, using the reported Dataflow output as the reproduction clue. Determine what environment or spec information is missing and verify that the resulting proto is valid for the affected runners.

Written by the indexing model from the issue text.