Fix incorrect example path and migration filename in docs

[toyeshhm]

Six documentation/comment corrections, two of which are wrong enough to mislead a reader following the docs.

src/macros/test.md — the #[sqlx::test] fixtures walkthrough points readers at examples/postgres/social-axum-with-tests, but the directory in this repo is examples/postgres/axum-social-with-tests. The two words are transposed, so anyone following the pointer hits a dead path.

sqlx-cli/README.md — the sqlx migrate add section says the new file is created at migrations/<timestamp>-<name>.sql. The separator is an underscore: sqlx-cli/src/migrate.rs builds the name with file_name.push('_'), and the reversible-migration example further down the same README already shows migrations/20211001154420_<name>.up.sql.

sqlx-postgres/src/options/pgpass.rs — the warning "Superfluous escape in in pgpass file" has a doubled in. The two sibling warnings in the same function ("Superfluous escape in pgpass file" and "Superfluous escape at EOL in pgpass file") are already correct, so this one is just a slip.

The rest are small:

• examples/sqlite/extension/sqlx.toml — "Provide the full path the the extension" → "the full path to the extension".
• examples/postgres/axum-social-with-tests/Cargo.toml — "Auxilliary" → "Auxiliary".
• sqlx-cli/tests/migrate.rs — doubled "to" in a comment.

No functional changes: the only non-comment edit is the text of one tracing::warn! string, which nothing asserts against.