Reduce console noise coming from unit tests:

A few unit tests have historically generated a lot of noise
to the console from log writes.  This noise was not useful
and made it harder to locate actual test failures.

By changing the log level of these tests from
- severities::kError to
- severities::kDisabled
it was possible to remove that noise coming from the logs.

src/test/rpc/ShardArchiveHandler_test.cpp

@@ -173,7 +173,8 @@ public:
         }
         c->setupControl(true, true, true);
 
-        jtx::Env env(*this, std::move(c));
+        jtx::Env env(
+            *this, std::move(c), nullptr, beast::severities::kDisabled);
 
         std::uint8_t const numberOfDownloads = 10;
 
@@ -276,7 +277,8 @@ public:
             }
             c->setupControl(true, true, true);
 
-            jtx::Env env(*this, std::move(c));
+            jtx::Env env(
+                *this, std::move(c), nullptr, beast::severities::kDisabled);
 
             std::uint8_t const numberOfDownloads = 10;
 
@@ -380,7 +382,8 @@ public:
         }
         c->setupControl(true, true, true);
 
-        jtx::Env env(*this, std::move(c));
+        jtx::Env env(
+            *this, std::move(c), nullptr, beast::severities::kDisabled);
         std::uint8_t const numberOfDownloads = 10;
 
         // Create some ledgers so that the ShardArchiveHandler