ci: Fix expected warnings file

The warning shown in gcc/doc/install.texi has been moved down slightly
due to adding new lines for the Rust documentation.

ChangeLog:

	* .github/bors_log_expected_warnings: Fix line number of install.texi warning.

.github/bors_log_expected_warnings

@@ -150,5 +150,5 @@ gengtype-lex.cc:357:15: warning: this statement may fall through [-Wimplicit-fal
 gengtype-lex.cc:357:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
 gengtype-lex.cc:357:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
 gengtype-lex.cc:357:15: warning: this statement may fall through [-Wimplicit-fallthrough=]
-install.texi:2231: warning: `.' or `,' must follow @xref, not f
+install.texi:2238: warning: `.' or `,' must follow @xref, not f
 libtool: install: warning: remember to run `libtool --finish /usr/local/libexec/gcc/x86_64-pc-linux-gnu/14.0.1'