fix: Memory leak in repo-server

[AJChandler]

This resolves a memory leak in the repo-server during plugin discovery caused by the connection not being closed.

Repo-Server Goroutines Leak

goroutine profile: total 1500
1458 @ 0x474eae 0x450a25 0x23d30ec 0x47d741
#	0x23d30eb	google.golang.org/grpc/internal/grpcsync.(*CallbackSerializer).run+0x10b	/go/pkg/mod/google.golang.org/grpc@v1.66.2/internal/grpcsync/callback_serializer.go:88

Repo-Server Goroutines Leak - Hard Refresh Applications x2

goroutine profile: total 4842
3138 @ 0x474eae 0x450a25 0x23d30ec 0x47d741
#	0x23d30eb	google.golang.org/grpc/internal/grpcsync.(*CallbackSerializer).run+0x10b	/go/pkg/mod/google.golang.org/grpc@v1.66.2/internal/grpcsync/callback_serializer.go:88

Fix Applied - Repo-Server Goroutines Leak - Hard Refresh Applications x2

Introduced by: #20196

Related improvement that would make this class of error harder to occur: #20217

This should be cherry-picked into the v2.13 release.

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I've updated both the CLI and UI to expose my feature, or I plan to submit a second PR with them.
• Does this PR require documentation updates?
• I've updated documentation as required by this PR.
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• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• My new feature complies with the feature status guidelines.
• I have added a brief description of why this PR is necessary and/or what this PR solves.
• Optional. My organization is added to USERS.md.
• Optional. For bug fixes, I've indicated what older releases this fix should be cherry-picked into (this may or may not happen depending on risk/complexity).

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.04%. Comparing base (fc9b33b) to head (3b07c91).
Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
util/app/discovery/discovery.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #20876      +/-   ##
==========================================
+ Coverage   55.00%   55.04%   +0.04%     
==========================================
  Files         324      324              
  Lines       55398    55400       +2     
==========================================
+ Hits        30471    30497      +26     
+ Misses      22309    22279      -30     
- Partials     2618     2624       +6     

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[crenshaw-dev]

/cherry-pick release-2.13