dgcov: parsing without dot to get specific version

- Regression introduced 7baf24a0 for multidigit gcc dump.
There is no dot in `dumpversion`.
```
$ gcc -dumpversion
10
```
Otherwise it will fail and not produce the output
```
Running dgcov
Name "IO::Uncompress::Gunzip::GunzipError" used only once: possible typo at ./dgcov.pl line 197.
Cannot parse gcc -dumpversion: 9
```

- The warning `once` is always generated:
```
Running dgcov
Name "IO::Uncompress::Gunzip::GunzipError" used only once: possible typo at ./dgcov.pl line 197.
<number>
```
Suppresing the line `Name "IO::Uncompress::Gunzip::GunzipError" used only once: possible typo at ./dgcov.pl line 197.`
with the patch.

- Reviewed by: <>

mysql-test/dgcov.pl

@@ -71,7 +71,7 @@ if ($opt_purge)
 }
 
 my $gcc_version= `gcc -dumpversion`;
-$gcc_version=~ s/^(\d+)\..*$/$1/ or die "Cannot parse gcc -dumpversion: $gcc_version";
+$gcc_version=~ s/^(\d+).*$/$1/ or die "Cannot parse gcc -dumpversion: $gcc_version";
 
 find(\&gcov_one_file, $root);
 find(\&write_coverage, $root) if $opt_generate;
@@ -191,6 +191,7 @@ sub gcov_one_file {
   } else {
     require IO::Uncompress::Gunzip;
     require JSON::PP;
+    no warnings 'once';
     my $gcov_file_json;
     s/\.gcda$// if $gcc_version >= 11;
     IO::Uncompress::Gunzip::gunzip("$_.gcov.json.gz", \$gcov_file_json)