Bump the rstudio.rstudio-workbench extension to 1.6.20 (#9688)

Updates the bundled `rstudio.rstudio-workbench` extension to version
1.6.20.

Package checksum:
`cfc8d2b15f991047a6169c422002505cc93aa04f33e2986319ef2d168a11a49c`
Commit:
[`d55e02c02814eb340dca8577da754fa5d546130a`](https://github.com/rstudio/rstudio-workbench-vscode-ext/commit/d55e02c02814eb340dca8577da754fa5d546130a)
Branch: `main`

**PR Reviewer**: before merging, please check out these changes locally,
run `detect-secrets` to [update the secrets baseline
file](https://github.com/posit-dev/positron/tree/main/build/secrets#updating-the-baseline-secrets-file),
audit the baseline file if necessary, and push the updates to the
secrets baseline file to this PR.

---------

Co-authored-by: posit-jenkins-enterprise[bot] <203673010+posit-jenkins-enterprise[bot]@users.noreply.github.com>
Co-authored-by: Jonathan McPherson <[email protected]>

Author: posit-jenkins-enterprise[bot]

build/secrets/.secrets.baseline

@@ -1145,7 +1145,7 @@
       {
         "type": "Hex High Entropy String",
         "filename": "product.json",
-        "hashed_secret": "5c6de360802015752ab1be5586a2a945488433ce",
+        "hashed_secret": "5b814ca57cd60fe405db9254ede91971a2e15767",
         "is_verified": false,
         "line_number": 114,
         "is_secret": false
@@ -1766,5 +1766,5 @@
       }
     ]
   },
-  "generated_at": "2025-09-29T20:57:53Z"
+  "generated_at": "2025-09-30T17:53:09Z"
 }

product.json

@@ -108,10 +108,10 @@
 		},
 		{
 			"name": "rstudio.rstudio-workbench",
-			"version": "1.6.17",
+			"version": "1.6.20",
 			"positUrl": "https://cdn.posit.co/pwb-components/extension",
 			"type": "reh-web",
-			"sha256": "bec52fc8978c76c7ee89ed8e66b19580db87d3e5c920d28fb6e82c26b06b086d",
+			"sha256": "cfc8d2b15f991047a6169c422002505cc93aa04f33e2986319ef2d168a11a49c",
 			"metadata": {
 				"publisherDisplayName": "Posit Software, PBC"
 			}