[CI] Pull in the latest mutes from base branch for PRs at runtime

.buildkite/hooks/pre-command

@@ -117,3 +117,7 @@ if [[ -f /etc/os-release ]] && grep -q '"Amazon Linux 2"' /etc/os-release; then
   echo "$(hostname -i | cut -d' ' -f 2)  $(hostname -f)." | sudo tee /etc/dnsmasq.hosts
   sudo systemctl restart dnsmasq.service
 fi
+
+if [[ "${BUILDKITE_PULL_REQUEST:-}" ]]; then
+  source .buildkite/scripts/get-latest-test-mutes.sh
+fi

build-tools-internal/src/main/java/org/elasticsearch/gradle/internal/test/MutedTestsBuildService.java

@@ -37,9 +37,9 @@ public abstract class MutedTestsBuildService implements BuildService<MutedTestsB
     public MutedTestsBuildService() {
         File infoPath = getParameters().getInfoPath().get().getAsFile();
         File mutedTestsFile = new File(infoPath, "muted-tests.yml");
-        excludePatterns.addAll(buildExcludePatterns(mutedTestsFile));
+        addExcludes(buildExcludePatterns(mutedTestsFile));
         for (RegularFile regularFile : getParameters().getAdditionalFiles().get()) {
-            excludePatterns.addAll(buildExcludePatterns(regularFile.getAsFile()));
+            addExcludes(buildExcludePatterns(regularFile.getAsFile()));
         }
     }
 
@@ -94,6 +94,16 @@ private List<String> buildExcludePatterns(File file) {
         return excludes;
     }
 
+    private void addExcludes(List<String> excludes) {
+        // Don't add the same exclude multiple times
+        for (String exclude : excludes) {
+            if (excludePatterns.stream().noneMatch(e -> e.equals(exclude))) {
+                excludePatterns.add(exclude);
+            }
+        }
+
+    }
+
     public interface Params extends BuildServiceParameters {
         RegularFileProperty getInfoPath();