Bump cosmos-sdk to v0.50.6

[pinosu]

No description provided.

[webmaster128]

We got a build fail here:

?       github.com/CosmWasm/wasmd/app/upgrades  [no test files]
?       github.com/CosmWasm/wasmd/cmd/wasmd     [no test files]
?       github.com/CosmWasm/wasmd/x/wasm/exported       [no test files]
?       github.com/CosmWasm/wasmd/x/wasm/keeper/wasmtesting     [no test files]
# github.com/CosmWasm/wasmd/x/wasm/types [github.com/CosmWasm/wasmd/x/wasm/types.test]
x/wasm/types/iavl_range_test.go:20:31: cannot use memdb (variable of type *"github.com/cosmos/cosmos-db".MemDB) as "github.com/cosmos/iavl/db".DB value in argument to iavl2.NewMutableTree: *"github.com/cosmos/cosmos-db".MemDB does not implement "github.com/cosmos/iavl/db".DB (wrong type for method Iterator)
                have Iterator([]byte, []byte) ("github.com/cosmos/cosmos-db".Iterator, error)
                want Iterator([]byte, []byte) ("github.com/cosmos/iavl/db".Iterator, error)
FAIL    github.com/CosmWasm/wasmd/x/wasm/types [build failed]

[pinosu]

We got a build fail here:

?       github.com/CosmWasm/wasmd/app/upgrades  [no test files]
?       github.com/CosmWasm/wasmd/cmd/wasmd     [no test files]
?       github.com/CosmWasm/wasmd/x/wasm/exported       [no test files]
?       github.com/CosmWasm/wasmd/x/wasm/keeper/wasmtesting     [no test files]
# github.com/CosmWasm/wasmd/x/wasm/types [github.com/CosmWasm/wasmd/x/wasm/types.test]
x/wasm/types/iavl_range_test.go:20:31: cannot use memdb (variable of type *"github.com/cosmos/cosmos-db".MemDB) as "github.com/cosmos/iavl/db".DB value in argument to iavl2.NewMutableTree: *"github.com/cosmos/cosmos-db".MemDB does not implement "github.com/cosmos/iavl/db".DB (wrong type for method Iterator)
                have Iterator([]byte, []byte) ("github.com/cosmos/cosmos-db".Iterator, error)
                want Iterator([]byte, []byte) ("github.com/cosmos/iavl/db".Iterator, error)
FAIL    github.com/CosmWasm/wasmd/x/wasm/types [build failed]

I will fix it now