Update release version to 0.26.5 (#6505)

# Description

Update release version to 0.26.5

## Type of change

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Fixes: #issue_number

## Auto-generated summary

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### <samp>🤖 Generated by Copilot at 2700a0c</samp>

### Summary
:arrow_up::bug::sparkles:

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Update the supported version of the `0.26` channel to `v0.26.5` in
`versions.yaml`. This aligns the channel with the latest release of the
radius project.

> _`0.26` channel_
> _Updated to the latest patch_
> _Autumn bugs are fixed_

### Walkthrough
* Update the supported version of the 0.26 channel to v0.26.5, the
latest release of the radius project
([link](https://github.com/radius-project/radius/pull/6505/files?diff=unified&w=0#diff-1c4cd801df522f4a92edbfb0fea95364ed074a391ea47c284ddc078f512f7b6aL3-R3))

docs/release-notes/v0.26.5.md

@@ -0,0 +1,11 @@
+## Radius v0.26.5
+
+This release addresses a CI/CD issue. Check out the [changelog](#changelog) for more details of what was addressed in this patch.
+
+## Changelog
+
+* Update release build by @sk593 in https://github.com/radius-project/radius/pull/6504
+
+**Full Changelog**: https://github.com/radius-project/radius/compare/v0.26.0...v0.26.5
+
+

versions.yaml

@@ -1,6 +1,6 @@
 supported:
   - channel: '0.26'
-    version: 'v0.26.4'
+    version: 'v0.26.5'
 deprecated:
   - channel: '0.25'
     version: 'v0.25.0'