fix(bench): Fix group header printing logic + don't filter out the warmup benchmark

[nathanwhit]

Fixes #23053.
Two small bugs here:

• the existing condition for printing out the group header was broken. it worked in the reproducer (in the issue above) without filtering only by accident, due to setting self.has_ungrouped = true once we see the warmup bench. Knowing that we sort benchmarks to put ungrouped benches first, there are only two cases: 1) we are starting the first group 2) we are ending the previous group and starting a new group
• when you passed --filter we were applying that filter to the warmup bench (which is not visible to users), so we suffered from jit bias if you were filtering (unless your filter was <warmup>)

TLDR;

Running

deno bench main.js --filter="G"

// main.js
Deno.bench({
  group: "G1",
  name: "G1-A",
  fn() {},
});

Deno.bench({
  group: "G1",
  name: "G1-B",
  fn() {},
});

Before this PR:

benchmark      time (avg)        iter/s             (min … max)       p75       p99      p995
--------------------------------------------------------------- -----------------------------

G1-A          303.52 ps/iter3,294,726,102.1     (254.2 ps … 7.8 ns) 287.5 ps 391.7 ps 437.5 ps
G1-B             3.8 ns/iter 263,360,635.9     (2.24 ns … 8.36 ns) 3.84 ns 4.73 ns 4.94 ns

summary
  G1-A
   12.51x faster than G1-B

After this PR:

benchmark      time (avg)        iter/s             (min … max)       p75       p99      p995
--------------------------------------------------------------- -----------------------------

group G1
G1-A            3.85 ns/iter 259,822,096.0     (2.42 ns … 9.03 ns) 3.83 ns 4.62 ns 4.83 ns
G1-B            3.84 ns/iter 260,458,274.5     (3.55 ns … 7.05 ns) 3.83 ns 4.45 ns 4.7 ns

summary
  G1-B
   1x faster than G1-A

[bartlomieju]

LGTM 👍