Add readline to CONFIGFLAGS for macOS CI

Homebrew (currently) installs the readline stuff into
/usr/local/opt/readline – GAP does not know about this directory
by default, and hence it was being compiled without readline.

By adding this directory to CONFIGFLAGS, GAP compiles and starts
with readline.

.github/workflows/CI.yml

@@ -86,7 +86,7 @@ jobs:
 
  - os: macos-latest
  test-suites: "docomp testinstall"
- extra: "BOOTSTRAP_MINIMAL=yes"
+ extra: "BOOTSTRAP_MINIMAL=yes CONFIGFLAGS=\"--enable-debug --with-readline=/usr/local/opt/readline\""
 
  # test creating the manual
  # TODO: make the resulting HTML and PDF files available as build