fish: avoid replacing "awk" in store paths

We encountered a fish build failure [1] caused by the store path for
gnugrep coincidentally containing the string `awk`. A later substitution
of `awk` replaced this substring with another store path in some files,
resulting in a number of broken paths.

Extending the `awk` pattern to `awk ` solves this problem and should be
relatively safe given that awk requires arguments to be passed.

[1] https://hydra.nixos.org/build/343861659

(cherry picked from commit c1d634b292)

pkgs/by-name/fi/fish/package.nix

@@ -254,14 +254,16 @@ stdenv.mkDerivation (finalAttrs: {
     EOF
   ''
   + lib.optionalString stdenv.hostPlatform.isLinux ''
+    # Trailing space in 'awk ' to avoid matching store paths that coincidentally
+    # contain the string 'awk'. (Yes, this has happened before!)
     for cur in share/functions/*.fish; do
       substituteInPlace "$cur" \
         --replace-quiet '/usr/bin/getent' '${lib.getExe getent}' \
-        --replace-quiet 'awk' '${lib.getExe' gawk "awk"}'
+        --replace-quiet 'awk ' '${lib.getExe' gawk "awk"} '
     done
     for cur in share/completions/*.fish; do
       substituteInPlace "$cur" \
-        --replace-quiet 'awk' '${lib.getExe' gawk "awk"}'
+        --replace-quiet 'awk ' '${lib.getExe' gawk "awk"} '
     done
   ''
   + ''