Fix OCSP timebomb in tests (#1891)

Resolves #1889

It turns out the first call to `OCSP_check_validity` in `TestGoodOCSP`
will emit two additional errors on to the error stack once the "this
update" field is outdated. Clearing the previous additional errors on
the stack allows us to check for which specific errors were emitted more
accurately.

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under the terms of the Apache 2.0 license and the ISC license.

crypto/ocsp/ocsp_test.cc

@@ -416,6 +416,7 @@ TEST(OCSPTest, TestGoodOCSP) {
   // This will cause the function to fail in two places, once when checking
   // if "(current_time + nsec) > thisupd [Status Not Yet Valid]", and a second
   // time when checking if "nextupd > (current_time - nsec) [Status Expired]".
+  ERR_clear_error();
   EXPECT_FALSE(OCSP_check_validity(thisupd, nextupd, -time(nullptr), -1));
   err = ERR_get_error();
   EXPECT_EQ(OCSP_R_STATUS_NOT_YET_VALID, ERR_GET_REASON(err));