fa9cb101cf refactor: Add explicit cast to expected_last_page to silence fuzz ISan (MarcoFalke)
Pull request description:
Fixes#30247
I don't think this implicit cast can lead to any bugs, so make it explicit to silence the fuzz integer sanitizer.
Can be tested with:
```
FUZZ=wallet_bdb_parser UBSAN_OPTIONS="suppressions=$(pwd)/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1" ./src/test/fuzz/fuzz /tmp/1376869be72eebcc87fe737020add634b1a29533
```
After downloading the raw fuzz input from 1376869be7
ACKs for top commit:
dergoegge:
utACK fa9cb101cf
Tree-SHA512: 226dcc58be8d70b4eec1657f232c9c6648b5dac5eb2706e7390e65ce0a031fbaf8afce97d71a535c8294467dca4757c96f294d8cc03d5e6a1c0a036b0e070325