Coverity CI: do not check coverity_token in every step

This reverts 960d231 (2022-02-21) because the commit 18f0496
(2022-04-20) already restricts the scheduled run to CESNET Git repository
or manual push.

So that the token unavailability should be considered error and thus the
condition doesn't need to be re-iterated in every step.

Author: MartinPulec

.github/workflows/coverity-scan.yml

@@ -16,16 +16,20 @@ jobs:
       coverity_token: ${{ secrets.coverity_token }}
 
     steps:
+    - name: Check Coverity token presence
+      if: env.coverity_token == ''
+      run: |
+              echo "secrects.coverity_token not present, skipping the analysys!"
+              exit 1
+
     - name: Get Coverity tool name # the file name contains version and is used as the cache key
-      if: ${{ env.coverity_token }}
       id: tool
       run: |
         FILENAME=$(curl -LIf "https://scan.coverity.com/download/linux64\
         ?token=$coverity_token&project=UltraGrid" |
         sed -n '/content-disposition/s/.*\"\(.*\)\"/\1/p')
         echo "filename=$FILENAME" >> $GITHUB_OUTPUT
     - name: Run actions/cache for Coverity build tool
-      if: ${{ env.coverity_token }}
       id: cache-coverity-tool
       uses: actions/cache@main
       with:
@@ -36,13 +40,11 @@ jobs:
       run: |
         wget --no-verbose https://scan.coverity.com/download/linux64 --post-data "token=$coverity_token&project=UltraGrid" -O ~/coverity_tool.tgz
     - name: Extract Coverity build tool
-      if: ${{ env.coverity_token }}
       run: |
         tar xaf ~/coverity_tool.tgz
         mv cov-analysis* /tmp/cov-analysis
 
     - uses: actions/checkout@v4
-      if: ${{ env.coverity_token }}
 
     - name: Fetch SDKs ETags
       id: etags
@@ -81,14 +83,11 @@ jobs:
            .github/scripts/Linux/prepare.sh
 
     - name: configure
-      if: ${{ env.coverity_token }}
       run: ./autogen.sh $FEATURES
     - name: Build with cov-build
-      if: ${{ env.coverity_token }}
       run: |
         /tmp/cov-analysis/bin/cov-build --dir cov-int make -j2
     - name: Submit the result to Coverity Scan
-      if: ${{ env.coverity_token }}
       run: |
         tar caf ultragrid.tar.xz cov-int
         result=$(curl -Sf --form token=$coverity_token \