Tests: Add "XCTSkipExhibits" call

A test fails in certain CI environmnents.  Introduce an `XCTExhibit...`
call that would skip a test if an environment variable is set.

Author: bkhouri

Sources/_InternalTestSupport/XCTAssertHelpers.swift

@@ -10,6 +10,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+import class Foundation.ProcessInfo
 import Basics
 #if os(macOS)
 import class Foundation.Bundle
@@ -322,3 +323,13 @@ public struct CommandExecutionError: Error {
     public let stdout: String
     public let stderr: String
 }
+
+
+public func XCTExhibitsGitHubIssue(_ number: Int) throws {
+    let envVar = "SWIFTCI_EXHIBITS_GH_\(number)"
+
+    try XCTSkipIf(
+        ProcessInfo.processInfo.environment[envVar] != nil,
+        "https://github.com/swiftlang/swift-package-manager/issues/\(number): \(envVar)environment variable is set"
+    )
+}

Tests/CommandsTests/PackageCommandTests.swift

@@ -4091,4 +4091,9 @@ class PackageCommandSwiftBuildTests: PackageCommandTestCase {
         try XCTSkipOnWindows(because: "TSCBasic/Path.swift:969: Assertion failed, https://github.com/swiftlang/swift-package-manager/issues/8602")
         try await super.testCommandPluginTargetBuilds()
     }
+
+    override func testCommandPluginPermissions() async throws {
+        try XCTExhibitsGitHubIssue(8782)
+        try await super.testCommandPluginPermissions()
+    }
 }