bug: this change raises a panic in store.SprintStoreOps

```
 go run ./gnovm/cmd/gno test -verbose ./examples/gno.land/p/demo/tests/ -run file/z0
?       ./examples/gno.land/p/demo/tests/subtests 	[no test files]
=== RUN   file/z0_filetest.gno
panic: expected JSON object but got "20"

goroutine 1 [running]:
github.com/gnolang/gno/tm2/pkg/amino.(*Codec).MustMarshalJSON(...)
	/home/tom/src/gno/tm2/pkg/amino/amino.go:818
github.com/gnolang/gno/tm2/pkg/amino.MustMarshalJSON({0xda1d40?, 0xc0001305a0?})
	/home/tom/src/gno/tm2/pkg/amino/amino.go:140 +0x53
github.com/gnolang/gno/gnovm/pkg/gnolang.StoreOp.String({0x0, {0x1026bf0, 0xc0001305a0}, {0x0, 0x0}})
	/home/tom/src/gno/gnovm/pkg/gnolang/store.go:654 +0xb2
github.com/gnolang/gno/gnovm/pkg/gnolang.(*defaultStore).SprintStoreOps(0xc0000166c0)
	/home/tom/src/gno/gnovm/pkg/gnolang/store.go:687 +0xff
github.com/gnolang/gno/gnovm/tests.RunFileTest({0xc000357158, 0x11}, {0xc0003691a0, 0x2e}, {0xc0001499e8, 0x1, 0x1013280?})
	/home/tom/src/gno/gnovm/tests/file.go:325 +0x44e
main.gnoTestPkg({0xc000116500, 0x20}, {0x0?, 0x0, 0x1?}, {0xc00035b720, 0x1, 0xc000129af8?}, 0xc00034c8c0, 0xc0002948c0)
	/home/tom/src/gno/gnovm/cmd/gno/test.go:337 +0x876
main.execTest(0xc00034c8c0, {0xc00035b590, 0x1, 0x1}, 0xc000036220?)
	/home/tom/src/gno/gnovm/cmd/gno/test.go:208 +0xb67
main.newTestCmd.func1({0x0?, 0x0?}, {0xc00035b590?, 0xc00035f118?, 0x0?})
	/home/tom/src/gno/gnovm/cmd/gno/test.go:51 +0x32
github.com/gnolang/gno/tm2/pkg/commands.(*Command).Run(0x5?, {0x1018768?, 0xc00003a130?})
	/home/tom/src/gno/tm2/pkg/commands/command.go:233 +0x1ac
github.com/gnolang/gno/tm2/pkg/commands.(*Command).Run(0xc00035ee70?, {0x1018768?, 0xc00003a130?})
	/home/tom/src/gno/tm2/pkg/commands/command.go:237 +0x154
github.com/gnolang/gno/tm2/pkg/commands.(*Command).ParseAndRun(0x4059dc?, {0x1018768, 0xc00003a130}, {0xc0000361f0?, 0x401240?, 0x0?})
	/home/tom/src/gno/tm2/pkg/commands/command.go:118 +0x4f
main.main()
	/home/tom/src/gno/gnovm/cmd/gno/main.go:14 +0x75
exit status 2
```

examples/gno.land/p/demo/tests/z0_filetest.gno

@@ -14,3 +14,6 @@ func main() {
 // Output:
 // 0
 // 1
+
+// Realm:
+// xxx