test_ukify: explicitly remove big temporary directories

pytest intentionally keeps around a limited number of the previous test
temporary directories [1]. This is generally OK, but in our tests that generate
initrds, we create a few very large files (both the initrd and kernel in a few
copies), which quickly adds up. I had a particularly large initrd (because of
some mkosi-initrd shenanigans), and I unded up with dozens of gigabytes of
temporary files from the tests. Let's just nuke the dirs where we write
kernel data.

[1] pytest-dev/pytest#543

(cherry picked from commit ef0a69e)
(cherry picked from commit d93341f)

Author: keszybz

src/ukify/test/test_ukify.py

@@ -431,6 +431,8 @@ def test_basic_operation(kernel_initrd, tmp_path):
     # let's check that objdump likes the resulting file
     subprocess.check_output(['objdump', '-h', output])
 
+    shutil.rmtree(tmp_path)
+
 def test_sections(kernel_initrd, tmp_path):
     if kernel_initrd is None:
         pytest.skip('linux+initrd not found')
@@ -459,6 +461,8 @@ def test_sections(kernel_initrd, tmp_path):
     for sect in 'text osrel cmdline linux initrd uname test'.split():
         assert re.search(fr'^\s*\d+\s+.{sect}\s+0', dump, re.MULTILINE)
 
+    shutil.rmtree(tmp_path)
+
 def test_addon(tmp_path):
     output = f'{tmp_path}/addon.efi'
     args = [
@@ -560,6 +564,8 @@ def test_efi_signing_sbsign(kernel_initrd, tmp_path):
 
         assert 'Signature verification OK' in dump
 
+    shutil.rmtree(tmp_path)
+
 def test_efi_signing_pesign(kernel_initrd, tmp_path):
     if kernel_initrd is None:
         pytest.skip('linux+initrd not found')
@@ -603,6 +609,8 @@ def test_efi_signing_pesign(kernel_initrd, tmp_path):
 
     assert f"The signer's common name is {author}" in dump
 
+    shutil.rmtree(tmp_path)
+
 def test_pcr_signing(kernel_initrd, tmp_path):
     if kernel_initrd is None:
         pytest.skip('linux+initrd not found')
@@ -666,6 +674,8 @@ def test_pcr_signing(kernel_initrd, tmp_path):
         assert list(sig.keys()) == ['sha1']
         assert len(sig['sha1']) == 4   # four items for four phases
 
+    shutil.rmtree(tmp_path)
+
 def test_pcr_signing2(kernel_initrd, tmp_path):
     if kernel_initrd is None:
         pytest.skip('linux+initrd not found')
@@ -736,6 +746,8 @@ def test_pcr_signing2(kernel_initrd, tmp_path):
     assert list(sig.keys()) == ['sha1']
     assert len(sig['sha1']) == 6   # six items for six phases paths
 
+    shutil.rmtree(tmp_path)
+
 def test_key_cert_generation(tmp_path):
     opts = ukify.parse_args([
         'genkey',