fix: secret reference update Ingress

[lingsamuel]

Type of change:

• Bugfix

Fixes #1777

What this PR does / why we need it:

Fix a bug that causes nil reference and secret change won't trigger Ingress resource sync.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #1780 (b63667e) into master (3a8fdf6) will increase coverage by 0.11%.
The diff coverage is 0.00%.

❗ Current head b63667e differs from pull request most recent head 0335372. Consider uploading reports for the commit 0335372 to get more accurate results

@@            Coverage Diff             @@
##           master    #1780      +/-   ##
==========================================
+ Coverage   39.30%   39.42%   +0.11%     
==========================================
  Files          91       91              
  Lines        8073     8049      -24     
==========================================
  Hits         3173     3173              
+ Misses       4494     4469      -25     
- Partials      406      407       +1     

Impacted Files	Coverage Δ
pkg/apisix/cluster.go	28.14% <ø> (ø)
...kg/providers/apisix/translation/apisix_consumer.go	65.21% <0.00%> (-1.95%)	⬇️
pkg/providers/ingress/ingress.go	4.98% <0.00%> (+0.44%)	⬆️
pkg/providers/ingress/translation/translator.go	0.00% <0.00%> (ø)

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[AlinsRan]

When deleting a secret, does the SSL object of APISIX exist?
Missing e2e case for delete-secret?