Travis: Enforce Coverity Scan on STATIC_CHECKS Linux/gcc build job

Also ensure that we are not using cached build objects (need to build
from scratch), and update encrypted Coverity Scan token.

.travis.yml

@@ -9,7 +9,7 @@ env:
     - SCONS_CACHE=$HOME/.scons_cache
     - SCONS_CACHE_LIMIT=1024
     - OPTIONS="verbose=yes progress=no gdnative_wrapper=yes"
-    - secure: "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"
+    - secure: AnjB84ZZYDxDQdWwsT9PJrD5tEnwcauzvVeSG+us2GxgfyJ2HFArkZ/IjlvbsfYIiiHghJ2Ssy9yPtUT921BtNNHoWuN/8YQziGrlwiSfLGmS/n8GFH22OYwzDSa7UC7ODts5La2I4+JzrdtF933TwE+4QzH4E3GyaKbznh402E=
 
 cache:
   directories:
@@ -19,7 +19,7 @@ matrix:
   include:
     - env: STATIC_CHECKS=yes
       os: linux
-      compiler: clang
+      compiler: gcc
     - env: GODOT_TARGET=x11 TOOLS=yes CACHE_NAME=${GODOT_TARGET}-gcc-tools"
       os: linux
       compiler: gcc
@@ -81,6 +81,16 @@ addons:
     build_command: "scons p=x11 -j2 $OPTIONS"
     branch_pattern: coverity_scan
 
+before_install:
+  - if [ "$STATIC_CHECKS" = "yes" ]; then
+      unset SCONS_CACHE;
+    else
+      if [ "$TRAVIS_BRANCH" = "coverity_scan" ]; then
+        echo "This job runs in the Coverity Scan branch and is not the STATIC_CHECKS job meant for it, so aborting with exit code 0.";
+        travis_terminate 0;
+      fi;
+    fi
+
 install:
   - if [ "$TRAVIS_OS_NAME" = "linux" ] && [ "$GODOT_TARGET" = "android" ]; then
       misc/travis/android-tools-linux.sh;