fix: use linguist-generated for language stats (#7685)

- Adds code comment to explain behavior of the `linguist-generated` gitattribute.
- Adjusts the code to ignore the file if `linguist-generated` is true.
- Resolves forgejo/forgejo#7677
- Adds unit testing.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7685
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/git/repo_language_stats_test.go

@@ -25,6 +25,15 @@ func TestRepository_GetLanguageStats(t *testing.T) {
 		"Python": 134,
 		"Java":   112,
 	}, stats)
+
+	stats, err = gitRepo.GetLanguageStats("95d3505f2db273e40be79f84416051ae85e9ea0d")
+	require.NoError(t, err)
+
+	assert.Equal(t, map[string]int64{
+		"Cobra":  67,
+		"Python": 67,
+		"Java":   112,
+	}, stats)
 }
 
 func TestMergeLanguageStats(t *testing.T) {