Improve performance of blob policy spec

What does this MR do and why?

This MR improves performance for blob policy spec by using let_it_be_with_reload combined with update! to avoid repetitive project factory creations.

RSpec Profiling

Here's the output from test-prof when run with FPROF=1. Note:

• Total amount of factories created went down from 119 to 37 🚀
• Total events went down from 5383 to 2511
• Queries saved: 2872

Before

[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:13.777 of 00:34.404 (40.05%)
Total events: 5383

Top 5 slowest suites (by time):

BlobPolicy (./spec/policies/blob_policy_spec.rb:5) – 00:13.777 (5383 / 42) of 00:34.404 (40.05%)



Finished in 46.38 seconds (files took 16.1 seconds to load)
42 examples, 0 failures

[TEST PROF INFO] Factories usage

 Total: 119
 Total top-level: 77
 Total time: 00:28.657 (out of 00:58.535)
 Total uniq factories: 4

   total   top-level     total time      time per call      top-level time               name

      42          42       24.4834s            0.5829s            24.4834s            project
      42           0        6.9447s            0.1653s             0.0000s          namespace
      34          34        4.1659s            0.1225s             4.1659s               user
       1           1        0.0082s            0.0082s             0.0082s            license

After

[TEST PROF INFO] EventProf results for sql.active_record

Total time: 00:06.227 of 00:19.857 (31.36%)
Total events: 2511

Top 5 slowest suites (by time):

BlobPolicy (./spec/policies/blob_policy_spec.rb:5) – 00:06.227 (2511 / 42) of 00:19.857 (31.36%)



Finished in 31.18 seconds (files took 15.81 seconds to load)
42 examples, 0 failures

[TEST PROF INFO] Factories usage

 Total: 37
 Total top-level: 36
 Total time: 00:10.541 (out of 00:43.007)
 Total uniq factories: 4

   total   top-level     total time      time per call      top-level time               name

      34          34        4.6442s            0.1366s             4.6442s               user
       1           1        0.0143s            0.0143s             0.0143s            license
       1           1        5.8826s            5.8826s             5.8826s            project
       1           0        0.3638s            0.3638s             0.0000s          namespace

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.