Test: Fix test in compactor/retention/expiration_test.go on slow machines

[piggynl]

What this PR does / why we need it:
The "just expired tenant" test requires the corresponding e.Expired to be called within 0.01ms with previous code, and which fails on low performance devices.

loki/pkg/storage/stores/shipper/compactor/retention/expiration_test.go

Lines 70 to 88 in ff47d74

	tests := []struct {
	name string
	ref ChunkEntry
	want bool
	}{
	{"expired tenant", newChunkEntry("1", `{foo="buzz"}`, model.Now().Add(-3*time.Hour), model.Now().Add(-2*time.Hour)), true},
	{"just expired tenant", newChunkEntry("1", `{foo="buzz"}`, model.Now().Add(-3*time.Hour), model.Now().Add(-1*time.Hour+(10*time.Microsecond))), false},
	{"not expired tenant", newChunkEntry("1", `{foo="buzz"}`, model.Now().Add(-3*time.Hour), model.Now().Add(-30*time.Minute)), false},
	{"not expired tenant by far", newChunkEntry("2", `{foo="buzz"}`, model.Now().Add(-72*time.Hour), model.Now().Add(-3*time.Hour)), false},
	{"expired stream override", newChunkEntry("2", `{foo="bar"}`, model.Now().Add(-12*time.Hour), model.Now().Add(-10*time.Hour)), true},
	{"non expired stream override", newChunkEntry("1", `{foo="bar"}`, model.Now().Add(-3*time.Hour), model.Now().Add(-90*time.Minute)), false},
	}
	for _, tt := range tests {
	t.Run(tt.name, func(t *testing.T) {
	actual, nonDeletedIntervals := e.Expired(tt.ref, model.Now())
	require.Equal(t, tt.want, actual)
	require.Nil(t, nonDeletedIntervals)
	})
	}

Which issue(s) this PR fixes:
None

Special notes for your reviewer:
None

Checklist

• Documentation added - not needed
• Tests updated
• Add an entry in the CHANGELOG.md about the changes.

[CLAassistant]

All committers have signed the CLA.

[cyriltovena]

LGTM