Disable pwsh installation tests in CYGWIN, MSYS, and MINGW.

There is no pwsh support there and if the installation test suite find the windows pwsh.exe it will fail due to IO issues.

testsuite/install.00-init/005-init_ts.exp

@@ -129,6 +129,14 @@ foreach shell [list sh bash basheu ksh zsh csh tcsh fish tcl perl python ruby cm
             set shellbin [find_bin ksh93]
          }
       }
+      pwsh {
+         # Don't test pwsh in cygwin or msys (pwsh.exe won't work properly)
+         if {![regexp "(CYGWIN|MINGW|MSYS_NT).*" $tcl_platform(os)]} {
+            set shellbin [find_bin pwsh]
+         } else {
+            set shellbin ""
+         }
+      }
       default {
          set shellbin [find_bin $shell]
       }