Refactor assert in scan_snapshot_stores()

[brooksprumo]

Problem

In #34118 we are upgrading Rust. The way Rust nightly displays panic messages has changed. This can cause should_panic tests to fail if they specify an expected message. We're seeing that in the accounts_db::tests::test_accountsdb_scan_snapshot_stores_illegal_range_xxx tests.

Here's what the error looks like:

test accounts_db::tests::test_accountsdb_scan_snapshot_stores_illegal_range_end - should panic ... FAILED

failures:

---- accounts_db::tests::test_accountsdb_scan_snapshot_stores_illegal_range_end stdout ----
thread 'accounts_db::tests::test_accountsdb_scan_snapshot_stores_illegal_range_end' panicked at accounts-db/src/accounts_db.rs:7644:9:
assertion failed: bin_range.start < bins && bin_range.end <= bins &&
    bin_range.start < bin_range.end
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
note: panic did not contain expected string
      panic message: `"assertion failed: bin_range.start < bins && bin_range.end <= bins &&\n    bin_range.start < bin_range.end"`,
 expected substring: `"bin_range.start < bins && bin_range.end <= bins &&\\n    bin_range.start < bin_range.end"`

Here's the build log: https://buildkite.com/solana-labs/solana/builds/104653#018be0ac-278d-4621-9fd4-629956045713

Since the newlines seem to be an issue, we can split up the assert so that the panic message doesn't have any newlines. There will be no functional difference.

Summary of Changes

Split the assert.

[codecov]

Codecov Report

Merging #34162 (8889a5f) into master (07f1709) will decrease coverage by 0.1%.
The diff coverage is 100.0%.

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #34162     +/-   ##
=========================================
- Coverage    81.9%    81.9%   -0.1%     
=========================================
  Files         819      819             
  Lines      220120   220122      +2     
=========================================
- Hits       180367   180333     -34     
- Misses      39753    39789     +36     

[HaoranYi]

lgtm. thanks!