Ensure prefix is picked up on Windows so pyrcc5 runs

[gillins]

Checklist

• [x] Used a fork of the feedstock to propose changes
• [x] Bumped the build number (if the version is unchanged)
• [x] Re-rendered with the latest conda-smithy (Use the phrase code>@<space/conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• [x] Ensured the license file is being packaged.

xref: https://github.com/conda-forge/qgis-feedstock/pull/86

In pyqt 5.9, pyrcc5 is now a .bat file. The path to Python is written into it during the build, but because there is no space after the @ symbol (I think) conda-build isn't picking up that this needs to be replaced at install time like it does on Unix.

I've also added a test that pyrcc5 actually runs.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[gillins]

@conda-forge-admin, please rerender

[ocefpaf]

Thanks @gillins!