parse_env_file discard utf8 bom (#2638)

* parse_env_file discard utf8 bom

* powershell 5 may add the BOM even when explicitly using utf8

* add test + apply to GITHUB_PATH as well

* fix it

* fix powershel 5 syntax

* misc

* fixup

* fix wrong subaction

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/runner/testdata/windows-prepend-path-powershell-5/push.yml

@@ -0,0 +1,34 @@
+on:
+  push:
+defaults:
+  run:
+    shell: powershell
+jobs:
+  test:
+    runs-on: windows-latest
+    steps:
+    - run: |
+        mkdir build
+        echo '@echo off' | Out-File -FilePath build/test.cmd -Encoding utf8
+        echo 'echo Hi' | Out-File -FilePath build/test.cmd -Encoding utf8 -Append
+        mkdir build2
+        echo '@echo off' | Out-File -FilePath build/test2.cmd -Encoding utf8
+        echo 'echo test2' | Out-File -FilePath build/test2.cmd -Encoding utf8 -Append
+    - run: |
+        echo '${{ tojson(runner) }}'
+        ls
+        echo '${{ github.workspace }}'
+      working-directory: ${{ github.workspace }}\build
+    - run: |
+        echo $env:GITHUB_PATH
+        echo '${{ github.workspace }}\build' | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
+        cat $env:GITHUB_PATH
+    - run: |
+        echo $env:PATH
+        test
+    - run: |
+        echo "PATH=$env:PATH;${{ github.workspace }}\build2" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
+    - run: |
+        echo $env:PATH
+        test
+        test2