install(PACKAGE_INFO): Fix error when usage requirements contain certain genex

Since commit 13c7bb5b0c (cmGeneratorExpression: Update strip function to
collect parsed expressions, 2025-04-08, v4.1.0-rc1~361^2~1), the logic
to strip generator expressions would error if the stripped expressions
were being collected and an expression without a `:` was found inside an
expression with a `:`. This resulted in an error when exporting a target
that contained such a generator expression in its link libraries or
compile definitions.

Address the error by checking whether the latest `$<` proceeded the
latest `:`.

Tests/RunCMake/string/GenexpStrip.cmake

@@ -35,3 +35,7 @@ test_strip( # Multiple case
   "1$<AND:1,0>2$<IF:$<$<BOOL:1>:$<CONFIG:RELEASE>>,TRUE,FALSE>3"
   "123"
 )
+test_strip( # No : inside of :
+  "$<1:$<SEMICOLON>>1"
+  "1"
+)