Count issues recorded without known tests. (#593)

This PR ensures that the total issue count presented at the end of a
test run includes issues that aren't attributable to specific tests.

Refines #592.

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/Events/Recorder/Event.HumanReadableOutputRecorder.swift

@@ -262,16 +262,18 @@ extension Event.HumanReadableOutputRecorder {
         }
 
       case let .issueRecorded(issue):
-        if let test {
-          let id = test.id.keyPathRepresentation
-          var testData = context.testData[id] ?? .init(startInstant: instant)
-          if issue.isKnown {
-            testData.knownIssueCount += 1
-          } else {
-            testData.issueCount += 1
-          }
-          context.testData[id] = testData
+        let id: [String] = if let test {
+          test.id.keyPathRepresentation
+        } else {
+          []
+        }
+        var testData = context.testData[id] ?? .init(startInstant: instant)
+        if issue.isKnown {
+          testData.knownIssueCount += 1
+        } else {
+          testData.issueCount += 1
         }
+        context.testData[id] = testData
 
       default:
         // These events do not manipulate the context structure.