apply dirty fix in biomart.yaml

the same fix as applied here:
snakemake-workflows/rna-seq-kallisto-sleuth@5bf0c52

original solution can be found here:
https://stackoverflow.com/a/77370920

workflow/envs/biomart.yaml

@@ -5,3 +5,7 @@ channels:
 dependencies:
   - bioconductor-biomart =2.56
   - r-tidyverse =2.0
+  # remove once we can update to bioconductor-biomart of the 3.18 release, which will
+  # include this proper fix for the underlying compatibility issue:
+  # https://github.com/Bioconductor/BiocFileCache/pull/50
+  - r-dbplyr=2.3.4