Mixed case request results in missing request parameters in generated code

Version: betterproto==2.0.0b3

Requests with capital letters in the name seem to cause an issue with constructing methods. The request parameters are not added to the method. e.g

proto file:
```
rpc TestCAPITALS(TestCAPITALSRequest) returns (TestCAPITALSResponse){}

message TestCAPITALSRequest{
string name = 1;
}

message TestCAPITALSResponse{}
```

generated class:
```
async def test_capitals(self) -> "TestCapitalsResponse":

request = TestCapitalsRequest()

return await self._unary_unary(
"/tumelo.transparency.v1.InstrumentPortfolioTransparency/TestCAPITALS",
request,
TestCapitalsResponse,
)
```
we would expect a `name` field in the request but it is not there