Fix VS insertion app.config push: drop spurious regex prefix and disambiguate build number (#15790)

The post-roslyn-tools step that pushes vstest.console/app.config and
revision.txt into the VS insertion PR has been silently failing on every
run since it landed.

Two compounding bugs in the source-commit resolution:

1. The primary regex matched 'Updated Updating VS Test Platform from'
   but roslyn-tools logs 'Updating VS Test Platform from' (no 'Updated'
   prefix). The primary path never fired, so the fallback always ran.

2. The fallback queried '/builds?buildNumber=20260514.9' and took
   value[0]. buildNumber is not unique across pipelines — on a typical
   day it matches builds from dotnet-roslyn, dotnet-runtime,
   microsoft-vstest, microsoft-testfx, dotnet-wpf, and several others.
   The fallback returned the first one (e.g. dotnet-roslyn), then tried
   to fetch app.config from the microsoft-vstest mirror at that
   unrelated SHA, failing with TF401029: GitCommitDoesNotExistException.

Drop the bogus 'Updated ' prefix from the primary regex (verified
against the actual log line in build 2975466) and filter the fallback
result by definition.name so the right pipeline is picked.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: nohwnd

azure-pipelines-insertion.yml

@@ -221,9 +221,9 @@ extends:
 
                         $sourceCommit = $null
 
-                        # Extract the build ID from the "Updated Updating VS Test Platform from [...] to [buildnum](url) ([sha](sourcesUrl))" line.
+                        # Extract the build ID from the "Updating VS Test Platform from [...] to [buildnum](url) ([sha](sourcesUrl))" line.
                         # We use the build ID to resolve the full commit SHA via the builds API.
-                        if ($outputText -match 'Updated Updating VS Test Platform from .+ to \[\S+\]\([^)]+\) \(\[[0-9a-f]{7,40}\]\(https://dev\.azure\.com/dnceng/[^)]+/_apis/build/builds/(\d+)/sources\)\)') {
+                        if ($outputText -match 'Updating VS Test Platform from .+ to \[\S+\]\([^)]+\) \(\[[0-9a-f]{7,40}\]\(https://dev\.azure\.com/dnceng/[^)]+/_apis/build/builds/(\d+)/sources\)\)') {
                           $sourceBuildId = $Matches[1]
                           Write-Host "Resolving source commit from build ID $sourceBuildId"
                           $buildUrl = "$dncengBase/_apis/build/builds/${sourceBuildId}?api-version=7.1"
@@ -232,14 +232,17 @@ extends:
                         }
 
                         if (-not $sourceCommit) {
-                          # Fallback: resolve source commit from build number via AzDO API
+                          # Fallback: resolve source commit from build number via AzDO API.
+                          # buildNumber is not unique across pipelines (e.g. "20260514.9" matches dotnet-roslyn,
+                          # dotnet-runtime, microsoft-vstest, ...) so filter the result by the mirror pipeline name.
                           if ($outputText -match 'Found microsoft-vstest build number (\S+)') {
                             $buildNumber = $Matches[1]
                             Write-Host "Resolving source commit from build number $buildNumber"
                             $buildsUrl = "$dncengBase/_apis/build/builds?buildNumber=$buildNumber&api-version=7.1"
                             $buildsResponse = Invoke-RestMethod -Uri $buildsUrl -Headers $dncengHeaders -Method Get
-                            if ($buildsResponse.value -and $buildsResponse.value.Count -gt 0) {
-                              $sourceCommit = $buildsResponse.value[0].sourceVersion
+                            $matchingBuild = $buildsResponse.value | Where-Object { $_.definition.name -eq $mirrorRepoId } | Select-Object -First 1
+                            if ($matchingBuild) {
+                              $sourceCommit = $matchingBuild.sourceVersion
                             }
                           }
                         }