tests: updated the nightly tests to use SST 13.0.0 (#441)

PR https://github.com/gem5/gem5/pull/396 updates the gem5 SST bridge to
use StandardMem in SST. This change updates the nightly tests to use SST
13.0.0 instead of SST 11.1.0. It also updates the dockerfile.

Change-Id: I5c109c40379d2f09601a1c9f19c51dd716c6582e

---------

Signed-off-by: Kaustav Goswami <kggoswami@ucdavis.edu>
Co-authored-by: Bobby R. Bruce <bbruce@ucdavis.edu>

.github/workflows/daily-tests.yaml

@@ -220,6 +220,9 @@ jobs:
                   ref: develop
             - name: Build RISCV/libgem5_opt.so with SST
               run: scons build/RISCV/libgem5_opt.so --without-tcmalloc --duplicate-sources --ignore-style -j $(nproc)
+            - name: Makefile ext/sst
+              working-directory: ${{ github.workspace }}/ext/sst
+              run: mv Makefile.linux Makefile
             - name: Compile ext/sst
               working-directory: ${{ github.workspace }}/ext/sst
               run: make -j $(nproc)