tests: use grep -F instead of obsolescent fgrep Testing on Fedora 38 failed with: fgrep: warning: fgrep is obsolescent; using grep -F The warning comes from https://git.savannah.gnu.org/cgit/grep.git/commit/?id=a9515624709865d480e3142fd959bccd1c9372d1 . For further anecdotal evidence of the change, see https://www.phoronix.com/news/GNU-Grep-3.8-Stop-egrep-fgrep . grep -F is POSIX, but there is a risk that it doesn't work the same on all platforms - especially older Unix versions. It should however always be possible to put a GNU grep in $PATH before running the tests.

--- a/contrib/check-code.py	Mon Jun 26 14:34:58 2023 +0200
+++ b/contrib/check-code.py	Mon Jun 26 14:54:00 2023 +0200
@@ -147,6 +147,7 @@
             '[ foo == bar ] is a bashism, use [ foo = bar ] instead',
         ),
         (r'(^|\|\s*)egrep', "use grep -E for extended grep syntax"),
+        (r'(^|\|\s*)fgrep', "use grep -F for fixed string grepping"),
         (r'(^|\|\s*)e?grep .*\\S', "don't use \\S in regular expression"),
         (r'(?<!!)/bin/', "don't use explicit paths for tools"),
         (r'#!.*/bash', "don't use bash in shebang, use sh"),