ci: allow powershell variables assigned in env scripts to persist

Load env scripts with `.` sourcing instead of `Invoke-Expression`.
This allows powershell variables to persist, much like bash.

Leave helper script loading unchanged, as those scripts may set
powershell variables that we do not want to persist.

.gitlab/ci/env.ps1

@@ -1,3 +1,3 @@
 if (Test-Path -Path ".gitlab/ci/env_$env:CMAKE_CONFIGURATION.ps1" -PathType Leaf) {
-  Invoke-Expression ".gitlab/ci/env_$env:CMAKE_CONFIGURATION.ps1"
+  . ".gitlab/ci/env_$env:CMAKE_CONFIGURATION.ps1"
 }

.gitlab/ci/env_windows_vs2022_x64_ninja.ps1

@@ -1,3 +1,3 @@
 if ("$env:CMAKE_CI_NIGHTLY" -eq "true") {
-  Invoke-Expression ".gitlab/ci/ispc-env.ps1"
+  . ".gitlab/ci/ispc-env.ps1"
 }

.gitlab/ci/env_windows_vs2022_x64_ninja_multi.ps1

@@ -1,5 +1,5 @@
 if ("$env:CMAKE_CI_NIGHTLY" -eq "true") {
-  Invoke-Expression -Command ".gitlab/ci/ispc-env.ps1"
+  . ".gitlab/ci/ispc-env.ps1"
 }
 
 $pwdpath = $pwd.Path

.gitlab/os-windows.yml

@@ -293,7 +293,7 @@
 ## Windows-specific scripts
 
 .before_script_windows: &before_script_windows
-    - Invoke-Expression -Command .gitlab/ci/env.ps1
+    - . .gitlab/ci/env.ps1
     - $pwdpath = $pwd.Path
     - powershell -File ".gitlab/ci/wix.ps1"
     - Set-Item -Force -Path "env:WIX" -Value "$pwdpath\.gitlab\wix"
@@ -352,7 +352,7 @@
     stage: test-ext
 
     script:
-        - Invoke-Expression -Command .gitlab/ci/env.ps1
+        - . .gitlab/ci/env.ps1
         - build/install/bin/ctest --output-on-failure -V -S .gitlab/ci/ctest_standalone.cmake
 
     interruptible: true