failures using extra/additional repository with trailing slash

[achubaty]

specifying additional cran-like repo with a trailing slash causes failures when installing packages (ℹ source packages are missing from predictiveecology.r-universe.dev).

> options(repos = c(PE = 'https://predictiveecology.r-universe.dev/'))
> pak::repo_ping()
Repository summary:                                source          
PE            @ predictiveecology.r-universe.dev     x        
CRAN          @ cran.rstudio.com                     ✓      (145ms)
BioCsoft      @ bioconductor.org                     ✓      (346ms)
BioCann       @ bioconductor.org                     ✓      (366ms)
BioCexp       @ bioconductor.org                     ✓      (580ms)
BioCworkflows @ bioconductor.org                     ✓      (449ms)

whereas, removing the trailing slash works:

> options(repos = c(PE = 'https://predictiveecology.r-universe.dev'))
> pak::repo_ping()
Repository summary:                                source          
PE            @ predictiveecology.r-universe.dev     ✓      (316ms)
CRAN          @ cran.rstudio.com                     ✓      (325ms)
BioCsoft      @ bioconductor.org                     ✓      (666ms)
BioCann       @ bioconductor.org                     ✓      (665ms)
BioCexp       @ bioconductor.org                     ✓      (885ms)
BioCworkflows @ bioconductor.org                     ✓      (863ms)