try to fix a flaky test

Author: yihui

tests/test-ci/test-install.R

@@ -1,8 +1,13 @@
 library(testit)
 
 assert('normalize_repo() creates a valid url', {
-  (normalize_repo('https://mirrors.mit.edu/CTAN/') %==%
-     'https://mirrors.mit.edu/CTAN/systems/texlive/tlnet')
+  u1 = 'https://mirrors.mit.edu/CTAN/'
+  # for some reason, normalize_repo() may not always work on certain platforms on GHA
+  for (i in 1:10) {
+    u2 = normalize_repo(u1)
+    if (u1 != u2) break else Sys.sleep(1)
+  }
+  (u2 %==% 'https://mirrors.mit.edu/CTAN/systems/texlive/tlnet')
   (normalize_repo('https://ftp.tu-chemnitz.de/pub/tug/historic/systems/texlive/2020/tlnet-final/') %==%
      'https://ftp.tu-chemnitz.de/pub/tug/historic/systems/texlive/2020/tlnet-final')
 })