Incorrect detection of pgpass file on non-Windows platform

The driver handles pgpass file incorrectly on non-Windows operating systems, it searches for pgpass.conf while it should take a look at .pgpass. The default file location works right and depends on platform.

[YohDeadfall]

Here is a history of this file:

1. Original version, environment variable was introduced in this repo in #1 and it was 3.2.

        internal static string? GetSystemPgPassFilePath()
        {
            var pgpassEnv = Environment.GetEnvironmentVariable("PGPASSFILE");
            if (pgpassEnv != null)
                return pgpassEnv;

            // ReSharper disable AssignNullToNotNullAttribute
            return PGUtil.IsWindows
                ? Path.Combine(Environment.GetEnvironmentVariable("APPDATA"), "postgresql", "pgpass.conf")
                : Path.Combine(Environment.GetEnvironmentVariable("HOME"), ".pgpass");
            // ReSharper restore AssignNullToNotNullAttribute
        }

1. Broken version by me.

        internal static string? GetSystemPgPassFilePath()
        {
            var pgpassEnv = Environment.GetEnvironmentVariable("PGPASSFILE");
            if (pgpassEnv != null)
                return pgpassEnv;

            return PGUtil.IsWindows
                ? Environment.GetEnvironmentVariable("APPDATA") is string appData ? Path.Combine(appData, "postgresql", "pgpass.conf") : null
                : Environment.GetEnvironmentVariable("HOME") is string home ? Path.Combine(home, "postgresql", "pgpass.conf") : null;
        }

1. Broken version refactored by @roji, so the bug was hidden.

        internal static string? GetSystemPgPassFilePath()
            => Environment.GetEnvironmentVariable("PGPASSFILE") ??
               (Environment.GetEnvironmentVariable(PGUtil.IsWindows ? "APPDATA" : "HOME") is string appData
                ? Path.Combine(appData, "postgresql", "pgpass.conf")
                : null);

1. Current version.

        internal static string? GetSystemPgPassFilePath()
            => Environment.GetEnvironmentVariable("PGPASSFILE") ?? (PGUtil.IsWindows
                ? Environment.GetEnvironmentVariable("APPDATA") is string appData ? Path.Combine(appData, "postgresql", "pgpass.conf") : null
                : Environment.GetEnvironmentVariable("HOME") is string home ? Path.Combine(home, "postgresql", ".pgpass") : null);

The bug was introduced in dev and backported to 4.1 via a rebase, so there is no breakage.

[roji]

FWIW we introduced pgpass support in 4.0 (#1442), but yeah, technically this is a breaking change.