ci(build): tolerate base-branch test failures in Coverage Base job

Merge-order races can leave the base branch with a pre-existing failing
test unrelated to the current PR (e.g. tronprotocol#6803 vs tronprotocol#6806 ordering). The
Coverage Base job only needs jacoco XML for coverage diffing, so a stale
test failure must not block the whole job.

Add continue-on-error: true to the Build (base) and Test with RocksDB
engine (base) steps, and relax if-no-files-found from error to warn so
that a compile-level failure degrades gracefully instead of producing a
misleading second failure.

Author: bladehan1

.github/workflows/pr-build.yml

@@ -260,9 +260,15 @@ jobs:
             coverage-base-x86_64-gradle-
 
       - name: Build (base)
+        # Test failures on the base branch are tolerated: merge-order races can
+        # leave the base with a pre-existing failing test that is unrelated to
+        # this PR.  The only output we need from this job is the jacoco XML for
+        # coverage diffing, so we must not let a stale test failure block it.
+        continue-on-error: true
         run: ./gradlew clean build --no-daemon --no-build-cache
 
       - name: Test with RocksDB engine (base)
+        continue-on-error: true
         run: ./gradlew :framework:testWithRocksDb --no-daemon --no-build-cache
 
       - name: Generate module coverage reports (base)
@@ -274,7 +280,7 @@ jobs:
           name: jacoco-coverage-base
           path: |
             **/build/reports/jacoco/test/jacocoTestReport.xml
-          if-no-files-found: error
+          if-no-files-found: warn
 
   coverage-gate:
     name: Coverage Gate