cmPackageInfoArguments: Improve error message

When given the name of a project that doesn't exist, report it as an
"unknown project" rather than an "invalid project". This is more
consistent with other, similar reporting.

Source/cmPackageInfoArguments.cxx

@@ -163,7 +163,7 @@ bool cmPackageInfoArguments::SetEffectiveProject(cmExecutionStatus& status)
   if (!this->ProjectName.empty()) {
     // User specified a project; make sure it exists.
     if (!mf.GetStateSnapshot().CheckProjectName(this->ProjectName)) {
-      status.SetError(cmStrCat(R"(PROJECT given invalid project name ")"_s,
+      status.SetError(cmStrCat(R"(PROJECT given unknown project name ")"_s,
                                this->ProjectName, R"(".)"_s));
       return false;
     }

Tests/RunCMake/ExportPackageInfo/BadArgs1-stderr.txt

@@ -17,6 +17,6 @@ Call Stack \(most recent call first\):
 
 
 CMake Error at BadArgs1\.cmake:6 \(export\):
-  export PROJECT given invalid project name "bar"\.
+  export PROJECT given unknown project name "bar"\.
 Call Stack \(most recent call first\):
   CMakeLists\.txt:3 \(include\)

Tests/RunCMake/InstallPackageInfo/BadArgs1-stderr.txt

@@ -17,6 +17,6 @@ Call Stack \(most recent call first\):
 
 
 CMake Error at BadArgs1\.cmake:6 \(install\):
-  install PROJECT given invalid project name "bar"\.
+  install PROJECT given unknown project name "bar"\.
 Call Stack \(most recent call first\):
   CMakeLists\.txt:3 \(include\)