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] https://github.com/pytest-dev/pytest/issues/543

src/ukify/test/test_ukify.py

@@ -438,6 +438,8 @@ 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')
@@ -466,6 +468,8 @@ 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+[0-9a-f]+', dump, re.MULTILINE)
 
+    shutil.rmtree(tmp_path)
+
 def test_addon(tmp_path):
     output = f'{tmp_path}/addon.efi'
     args = [
@@ -572,6 +576,8 @@ def test_efi_signing_sbsign(days, 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')
@@ -615,6 +621,8 @@ 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_inspect(kernel_initrd, tmp_path, capsys):
     if kernel_initrd is None:
         pytest.skip('linux+initrd not found')
@@ -660,6 +668,7 @@ def test_inspect(kernel_initrd, tmp_path, capsys):
     expected_linux = '.linux:\n  size:'
     assert expected_linux in text
 
+    shutil.rmtree(tmp_path)
 
 def test_pcr_signing(kernel_initrd, tmp_path):
     if kernel_initrd is None:
@@ -724,6 +733,8 @@ 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')
@@ -794,6 +805,8 @@ 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',