gnu: pigx-scrnaseq: Use older loompy.

* gnu/packages/bioinformatics.scm (pigx-scrnaseq)[inputs]: Replace
python-loompy with python-loompy-for-pigx-scrnaseq.

gnu/packages/bioinformatics.scm

@@ -12825,7 +12825,7 @@ (define-public pigx-scrnaseq
        ("python-pandas" ,python-pandas)
        ("python-magic" ,python-magic)
        ("python-numpy" ,python-numpy)
-       ("python-loompy" ,python-loompy)
+       ("python-loompy" ,python-loompy-for-pigx-scrnaseq)
        ("ghc-pandoc" ,ghc-pandoc)
        ("ghc-pandoc-citeproc" ,ghc-pandoc-citeproc)
        ("samtools" ,samtools)