ci: install lcov and valgrind in CI jobs

The fastsync-ci:v7 container does not include lcov or valgrind.
Add apt-get install steps to the coverage and valgrind jobs.

Also update lcov flags for lcov 2.x compatibility:
--rc lcov_branch_coverage=1 -> --branch-coverage

.gitea/workflows/ci.yaml

@@ -64,6 +64,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Install lcov
+        run: apt-get update -qq && apt-get install -y -qq lcov
+
       - name: Configure
         run: cmake -B build -S . -DENABLE_COVERAGE=ON -DSTRICT_WARNINGS=ON
 
@@ -75,8 +78,8 @@ jobs:
 
       - name: Coverage Report
         run: |
-          lcov --capture --directory build --output-file coverage.info --rc lcov_branch_coverage=1
-          lcov --remove coverage.info '/usr/*' '*/tests/*' '*/xxhash/*' --output-file coverage.info
+          lcov --capture --directory build --output-file coverage.info --branch-coverage
+          lcov --remove coverage.info '/usr/*' '*/tests/*' '*/xxhash/*' --output-file coverage.info --branch-coverage
           lcov --list coverage.info
 
   valgrind:
@@ -87,6 +90,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
+      - name: Install valgrind
+        run: apt-get update -qq && apt-get install -y -qq valgrind
+
       - name: Configure
         run: cmake -B build -S . -DSTRICT_WARNINGS=ON