Bump iffy/install-nim from 4 to 5

Bumps [iffy/install-nim](https://github.com/iffy/install-nim) from 4 to 5.
- [Release notes](https://github.com/iffy/install-nim/releases)
- [Changelog](https://github.com/iffy/install-nim/blob/master/CHANGELOG.md)
- [Commits](iffy/install-nim@v4...v5)

---
updated-dependencies:
- dependency-name: iffy/install-nim
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/tests.yml

@@ -29,7 +29,7 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - uses: iffy/install-nim@v4
+      - uses: iffy/install-nim@v5
         with:
           version: ${{ matrix.nimversion }}
         env: