Auto merge of #11885 - jdm:openssl-serial, r=ConnorGBrewster

Fix common OpenSSL intermittent failure on automated builders

OpenSSL requires that the digits of the serial number for the generated certs contain an even number of digits. The recent change in sslutils (b388d6b14d) does not fulfill this requirement. I'll be making the same PR upstream to address that, but this will get us out of the woods locally.

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<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #11858 and fix #11859
- [X] These changes do not require tests because there's no automated testing for the SSL cert generation

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tests/wpt/web-platform-tests/tools/sslutils/openssl.py

@@ -252,7 +252,10 @@ class OpenSSLEnvironment(object):
         with open(path("index.txt"), "w"):
             pass
         with open(path("serial"), "w") as f:
-            f.write(str(random.randint(0, 1000000)))
+            serial = str(random.randint(0, 1000000))
+            if len(serial) % 2:
+                serial = "0" + serial
+            f.write(serial)
 
         self.path = path