Use more distinct characters for 'skip' and 'pass w/known issues' symbols (#983)

This refines the characters used for the `.fail` and
`.pass(knownIssueCount:)` symbols to make them more distinct, especially
when rendered in a console without ANSI colors enabled.

### 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: stmontgomery

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

@@ -62,7 +62,7 @@ extension Event.Symbol {
       ("\u{10065F}", "arrow.triangle.turn.up.right.diamond.fill")
     case let .pass(knownIssueCount):
       if knownIssueCount > 0 {
-        ("\u{100884}", "xmark.diamond.fill")
+        ("\u{100883}", "xmark.diamond")
       } else {
         ("\u{10105B}", "checkmark.diamond.fill")
       }
@@ -118,8 +118,8 @@ extension Event.Symbol {
       // Unicode: WHITE DIAMOND
       return "\u{25C7}"
     case .skip:
-      // Unicode: HEAVY BALLOT X
-      return "\u{2718}"
+      // Unicode: HEAVY ROUND-TIPPED RIGHTWARDS ARROW
+      return "\u{279C}"
     case let .pass(knownIssueCount):
       if knownIssueCount > 0 {
         // Unicode: HEAVY BALLOT X
@@ -156,8 +156,8 @@ extension Event.Symbol {
       // Unicode: LOZENGE
       return "\u{25CA}"
     case .skip:
-      // Unicode: MULTIPLICATION SIGN
-      return "\u{00D7}"
+      // Unicode: HEAVY ROUND-TIPPED RIGHTWARDS ARROW
+      return "\u{279C}"
     case let .pass(knownIssueCount):
       if knownIssueCount > 0 {
         // Unicode: MULTIPLICATION SIGN