Use double quotes "" to allow substitution

Also remove an extraneous space in tests/oss-fuzz/build.sh.

.github/workflows/ci-unix-static-sanitized.yml

diff --git a/.github/workflows/ci-unix-static-sanitized.yml b/.github/workflows/ci-unix-static-sanitized.yml
index 73031c5..45d8502 100644
--- a/.github/workflows/ci-unix-static-sanitized.yml
+++ b/.github/workflows/ci-unix-static-sanitized.yml
@@ -47,7 +47,7 @@
         if: steps.cache-ext.outputs.cache-hit != 'true'
         working-directory: ./ext
         run: >
-          sed -i -e 's/meson setup \(.*\) \.\./meson setup \1 '"-Db_sanitize=${{ matrix.sanitizer }} -Db_lundef=false"' ../g' dav1d.cmd
+          sed -i -e 's/meson setup \(.*\) \.\./meson setup \1 -Db_sanitize=${{ matrix.sanitizer }} -Db_lundef=false ../g' dav1d.cmd
 
           ./dav1d.cmd
       - name: Build libyuv

tests/oss-fuzz/build.sh

diff --git a/tests/oss-fuzz/build.sh b/tests/oss-fuzz/build.sh
index 7af3cc0..517cad8 100755
--- a/tests/oss-fuzz/build.sh
+++ b/tests/oss-fuzz/build.sh
@@ -49,7 +49,7 @@
 then
   DAV1D_EXTRA_FLAGS="${DAV1D_EXTRA_FLAGS} -Denable_asm=false"
 fi
-sed -i 's/meson setup \(.*\) \.\./meson setup \1 '"${DAV1D_EXTRA_FLAGS}"' ../g' ./ext/dav1d.cmd
+sed -i "s/meson setup \(.*\) \.\./meson setup \1${DAV1D_EXTRA_FLAGS} ../g" ./ext/dav1d.cmd
 
 # Build libaom with sanitizer flags.
 # Adds extra flags: -DAOM_TARGET_CPU=generic for msan.