Stop printing a trailing space after PUBLIC in GRANT and REVOKE

[LucaCappelletti94]

Display for Grantee wrote the grantee type keyword with a trailing space baked in, then appended the name. PUBLIC is the only grantee type the parser ever builds without a name, so for it the space had nothing to follow it and GRANT SELECT ON t TO PUBLIC printed with a trailing space, which does not match the input it was parsed from.

The separator now belongs to the name rather than the keyword, so it is only written when a name follows.

[ting-hong-shieh]

Verified this against main at 2f3b5b82. The trailing space reproduces, and the fix is correct.

One case worth adding to the test: the same bug shows up mid-statement, which is the more damaging form. On the merge base:

GRANT SELECT ON t TO PUBLIC, ROLE r
  ->  GRANT SELECT ON t TO PUBLIC , ROLE r

With this PR it round-trips unchanged. A trailing space is easy to miss, but a space before the comma corrupts generated SQL visibly. Since verified_stmt("GRANT SELECT ON t TO PUBLIC") still passes when only the end-of-statement case is handled, a multi-grantee case would guard the part that matters most:

all_dialects_except(|d| d.is::<MsSqlDialect>())
    .verified_stmt("GRANT SELECT ON t TO PUBLIC, ROLE r");

Two things I checked while reviewing:

• PUBLIC really is the only grantee type the parser builds without a name — parse_grantees takes Some(name) in every other branch (src/parser/mod.rs:17758). The change does also drop the trailing space for any other type with name: None, but that is only reachable by building the AST directly, and the new output is right there too.
• The MsSqlDialect exclusion is load-bearing: with it removed the test fails, because MsSql parses PUBLIC as grantee_type: None, name: Some("PUBLIC") while PostgreSQL gives grantee_type: Public, name: None.

cargo test --all-features at 9d5f8e21: 1584 passed, 0 failed. cargo fmt --all -- --check and cargo clippy --all-targets --all-features -- -D warnings both clean.