vt: get rid of log spam on tests

Zig 0.16.0 made the criteria for reporting "failed command" stricter (or
looser, depending on your perspective I guess...) - now, tests that
print anything to stderr cause the message to appear.

Note that in this instance tests still pass and you get a return code of
0, but nonetheless, it can be confusing.

Additionally, having spammy passing tests in general is not necessarily
a great experience, so this should help with that.

Note that this change was already done to the main tests. We can add a
build argument to control this if need be.

src/lib_vt.zig

@@ -386,6 +386,12 @@ pub const std_options: std.Options = opts: {
 };
 
 test {
+    // Zig 0.16.0 has made test logging more strict. Now, *anything* that gets
+    // printed to stderr results in a "failed command" message, even if the
+    // tests ultimately passed. To reduce confusion here (and honestly, test
+    // log spam in general), we bump the default testing log level to error.
+    @import("std").testing.log_level = std.log.Level.err;
+
     _ = terminal;
     _ = @import("lib/main.zig");
     @import("std").testing.refAllDecls(input);