fix(main/fish): prepend @TERMUX_PREFIX@ to /bin/sh in two files

- Fixes https://github.com/termux/termux-packages/issues/27210

- I searched through the code and did some calculations, and as far as I can tell, these two instances of `/bin/sh` seem to be the only ones that are highly likely to produce the error on affected devices.

packages/fish/0010-fix-some-absolute-paths.patch

@@ -0,0 +1,22 @@
+--- a/share/functions/fish_update_completions.fish
++++ b/share/functions/fish_update_completions.fish
+@@ -26,7 +26,7 @@ function fish_update_completions --description "Update man-page based completion
+             # Orphan the job so that it continues to run in case of an early exit (#6269)
+             # Note that some distros split the manpage completion script out (#7183).
+             # In that case, we silence Python's failure.
+-            /bin/sh -c '
++            @TERMUX_PREFIX@/bin/sh -c '
+                 c=$(cat)
+                 ( printf %s "$c" | "$@" ) >/dev/null 2>&1 &
+             ' -- $update_argv $argv
+--- a/share/functions/help.fish
++++ b/share/functions/help.fish
+@@ -228,7 +228,7 @@ chromium-browser
+         # The space before the /c is to prevent msys2 from expanding it to a path
+         $fish_browser " /c" start $page_url
+     else if contains -- $fish_browser[1] $graphical_browsers
+-        /bin/sh -c '( "$@" ) &' -- $fish_browser $page_url
++        @TERMUX_PREFIX@/bin/sh -c '( "$@" ) &' -- $fish_browser $page_url
+     else
+         $fish_browser $page_url
+     end

packages/fish/build.sh

@@ -3,6 +3,7 @@ TERMUX_PKG_DESCRIPTION="The user-friendly command line shell"
 TERMUX_PKG_LICENSE="GPL-2.0"
 TERMUX_PKG_MAINTAINER="@termux"
 TERMUX_PKG_VERSION="4.2.0"
+TERMUX_PKG_REVISION=1
 TERMUX_PKG_SRCURL=https://github.com/fish-shell/fish-shell/releases/download/$TERMUX_PKG_VERSION/fish-${TERMUX_PKG_VERSION}.tar.xz
 TERMUX_PKG_SHA256=6c43be5a9274963c06ba4cd55a109dfcc4d5d3a8054ed0e0a3666388581ec252
 TERMUX_PKG_AUTO_UPDATE=true