FRED: Failed to open [...] HTTP/2 stream 1 was not closed cleanly

Noticed this since last week:

```
> getSymbols(Symbols="CPIAUCSL", src="FRED")

Error in getSymbols.FRED(Symbols = "CPIAUCSL", env = , verbose = FALSE, :
Unable to import “CPIAUCSL”.
cannot open the connection
In addition: Warning message:
Failed to open 'https://fred.stlouisfed.org/graph/fredgraph.csv?id=CPIAUCSL': HTTP/2 stream 1 was not closed cleanly: INTERNAL_ERROR (err 2)
```

I'm in a country that has rather unusual internet filtering. Yet with VPN it doesn't go away. This still works, which rules out a BLS-style anti-robot policy.

```
wget https://fred.stlouisfed.org/graph/fredgraph.csv?id=CPIAUCSL
```

I'm on quantmod 0.4.28.

Start at quantmod's getSymbols.FRED entry point and reproduce the CPIAUCSL request to https://fred.stlouisfed.org/graph/fredgraph.csv?id=CPIAUCSL. Compare its request behavior with the working wget command; done means getSymbols(Symbols="CPIAUCSL", src="FRED") imports the data without the HTTP/2 stream error.

Written by the indexing model from the issue text.