Auto merge of #15243 - UK992:windows-builder, r=larsbergstrom

Upload MSVC nightlies via MSYS environment

Follow-up to servo/saltfs#572

r? @larsbergstrom

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etc/ci/buildbot_steps.yml

@@ -128,4 +128,4 @@ windows-gnu-nightly:
 windows-msvc-nightly:
   - mach.bat build --release
   - mach.bat package --release
-  - .\etc\ci\upload_nightly.sh windows-msvc
+  - bash -l ./etc/ci/upload_nightly.sh windows-msvc