test(r/demo/tests): add filetest for PrevRealm

[grepsuzette]

PrevRealm was tested from gno/examples/gno.land/r/demo/tests/tests_test.gnotest. As far as I can see in r/demo/tests however, it was not tested for filetests.

Although gno test . passes, depending on whether #1704 is confirmed, there may be more filetests to add in this folder (in a different PR I guess).

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 47.58%. Comparing base (b965e5e) to head (9eb8476). Report is 33 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1705      +/-   ##
==========================================
+ Coverage   47.47%   47.58%   +0.11%     
==========================================
  Files         385      389       +4     
  Lines       61377    61593     +216     
==========================================
+ Hits        29140    29312     +172     
- Misses      29802    29833      +31     
- Partials     2435     2448      +13     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[grepsuzette]

I don't understand why the test fails with

PASS
coverage: 33.3% of statements
ok  	github.com/gnolang/gno/tm2/pkg/bft/rpc/lib/types	0.005s	coverage: 33.3% of statements
	github.com/gnolang/gno/tm2/pkg/bft/rpc/test		coverage: 0.0% of statements
# github.com/jmhodges/levigo
Error: ../../../../go/pkg/mod/github.com/jmhodges/[email protected]/batch.go:4:11: fatal error: leveldb/c.h: No such file or directory
    4 | // #include "leveldb/c.h"
      |           ^~~~~~~~~~~~~
compilation terminated.
Error: The operation was canceled.

[grepsuzette]

Did rebase and checks now pass. This PR should be good to go.