gnu: Adjust for python-build-system behavior change.

Commit cb72f9a773 changed the semantics of
SITE-PACKAGES, but did not adjust all callers.

* gnu/packages/bioinformatics.scm (python-pyvcf)[arguments]: Adjust for
missing trailing slash.
* gnu/packages/maths.scm (nomad-optimizer)[arguments]: Likewise.
* gnu/packages/patchutils.scm (patchwork)[arguments]: Likewise.

gnu/packages/bioinformatics.scm

@@ -15281,8 +15281,7 @@ (define-public python-pyvcf
             (lambda* (#:key inputs outputs #:allow-other-keys)
               (delete-file-recursively (string-append
                                          (site-packages inputs outputs)
-                                         "vcf/test"))
-              #t)))))
+                                         "/vcf/test")))))))
     (native-inputs `(("python-cython" ,python-cython)))
     (propagated-inputs
      `(("python-pysam" ,python-pysam)

gnu/packages/maths.scm

@@ -2009,7 +2009,7 @@ (define-public nomad-optimizer
            (lambda* (#:key inputs outputs #:allow-other-keys)
              (delete-file (string-append
                            (site-packages inputs outputs)
-                           "PyNomad-0.0.0-py"
+                           "/PyNomad-0.0.0-py"
                            (python-version (assoc-ref inputs "python"))
                            ".egg-info"))
              #t)))))

gnu/packages/patchutils.scm

@@ -390,7 +390,7 @@ (define pythonpath
                (for-each (lambda (directory)
                            (copy-recursively
                             directory
-                            (string-append out-site-packages directory)))
+                            (string-append out-site-packages "/" directory)))
                          '(;; Contains the python code
                            "patchwork"
                            ;; Contains the templates for the generated HTML
@@ -403,9 +403,9 @@ (define pythonpath
                            (install-file file (string-append out "/bin")))
                          (list
                           (string-append out-site-packages
-                                         "patchwork/bin/parsemail.sh")
+                                         "/patchwork/bin/parsemail.sh")
                           (string-append out-site-packages
-                                         "patchwork/bin/parsemail-batch.sh")))
+                                         "/patchwork/bin/parsemail-batch.sh")))
 
                ;; Collect the static assets, this includes JavaScript, CSS and
                ;; fonts. This is a standard Django process when running a