processor_attributes: fix warnings

[nokute78]

This patch is to fix following warnings.

 [ 57%] Building C object plugins/processor_attributes/CMakeFiles/flb-plugin-processor_attributes.dir/attributes.c.o
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c: In function ‘attribute_match_cb’:
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:829:43: warning: passing argument 2 of ‘span_contains_attribute’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  829 |         if (span_contains_attribute(span, name) == FLB_TRUE) {
      |                                           ^~~~
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:676:42: note: expected ‘char *’ but argument is of type ‘const char *’
  676 |                                    char *name)
      |                                    ~~~~~~^~~~
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:830:41: warning: passing argument 2 of ‘span_remove_attribute’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  830 |             span_remove_attribute(span, name);
      |                                         ^~~~
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:686:40: note: expected ‘char *’ but argument is of type ‘const char *’
  686 |                                  char *name)
      |                                  ~~~~~~^~~~
/home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:833:45: warning: passing argument 2 of ‘ctr_span_set_attribute_string’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  833 |         ctr_span_set_attribute_string(span, name, temporary_value);
      |                                             ^~~~
In file included from /home/taka/git/fluent-bit/lib/ctraces/include/ctraces/ctraces.h:84,
                 from /home/taka/git/fluent-bit/include/fluent-bit/flb_processor.h:29,
                 from /home/taka/git/fluent-bit/include/fluent-bit/flb_processor_plugin.h:24,
                 from /home/taka/git/fluent-bit/plugins/processor_attributes/attributes.c:25:
/home/taka/git/fluent-bit/lib/ctraces/include/ctraces/ctr_span.h:120:67: note: expected ‘char *’ but argument is of type ‘const char *’
  120 | int ctr_span_set_attribute_string(struct ctrace_span *span, char *key, char *value);
      |                                                             ~~~~~~^~~

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• [N/A] Backport to latest stable release.

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[cosmo0920]

Hi @nokute78!
We decided to remove processor_attributes and processor_content_modifier is a successor of it. So, if you have a cycle, could you take a look the successor plugin instead?

[nokute78]

@cosmo0920 Thank you for information.
I built processor_content_modifier and there were no warnings.
So I close this PR.