translation: mark vim.pot as binary

`vim.pot` is included in the repository after

```gitcommit
commit 59bd74e
Author: Christian Brabandt <[email protected]>
Date:   Sun Jul 13 08:26:57 2025 +0200

    translation: include vim.pot in the repository
```

And it adds quite a lot of noise to the diffs since then.  See the
reasoning in a comment in `.gitattributes`.

I'm not 100% sure that marking it as binary would have no negative side
effects.  But I was not able to find a better option in `git help
attributes`.

Solution suggested in

```gitcommit
commit 5d552d6
Author: Christian Brabandt <[email protected]>
Date:   Tue Jul 15 20:42:48 2025 +0200

    translation: ignore vim.pot creation date, regenerate it, rm allfiles

    Signed-off-by: Christian Brabandt <[email protected]>
```

does not seem to be solving the problem.  It only hides the
`POT-Creation` line from the `vim.pot` diff.  Maybe a more elaborate
filter could be used - one that replaces lines numbers in `vim.pot` with
`xxxx`, thus removing the most annoying and useless part of the diff.

One downside is that it requires everyone to install such a filter
locally - it can not be part of the repo config, as far as I understand.

closes: #17775

Signed-off-by: Illia Bobyr <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: illia-bobyr

.gitattributes

@@ -1,11 +1,25 @@
 src/testdir/test42.in diff
 
-# vim.pot may change just by incrementing a patch number
-# so ignore the following differences:
+# `vim.pot` is updated every time any of the *.c files are modified.  And as it
+# contains line numbers for strings from *.c files, inserting a line into a
+# single .c file may cause many lines in the `vim.pot` file to be updated.
+#
+# This generates a lot of "noise" in the diffs.  And especially considering that
+# `vim.pot` is a generated file, looking at changes in this file is not useful.
+#
+# By marking it as binary we tell the git machinery that it should not be
+# presented to the user in patches, use "git diff --text" to override
+src/po/vim.pot -diff
+
+# Although vim.pot has been marked as binary, you may want to check the textual differences
+# using git --text but still want to ignore some noisy output like:
 # - POT-Creation Date
 # - comments pointing to the message source location in
 #   *.c/*.h/*.vim/*.cpp/*.in/*.xs files followed by line numbers
-# set this up using:
+# Note: location comments should be no longer part of vim.pot, since commit 2844765e903214490e1
+# which add the --no-location argument for xgettext to no longer ouput such comments
+#
+# To ignore certain changes, setup a custom textconv filter using:
 # git config diff.ignore_vim_pot.textconv "grep -Ev '^.(POT-Creation-Date:|.*\\.([ch]|vim|in|xs|cpp):).*$'"
 src/po/vim.pot diff=ignore_vim_pot